diff --git a/ABC451/oni0nfr1/A.rs b/ABC451/oni0nfr1/A.rs
new file mode 100644
index 0000000..bf3f457
--- /dev/null
+++ b/ABC451/oni0nfr1/A.rs
@@ -0,0 +1,26 @@
+use std::{
+    io::{self, Read},
+    str::{FromStr, SplitWhitespace},
+};
+
+fn read_value<T>(tokens: &mut SplitWhitespace<'_>) -> Option<T>
+where
+    T: FromStr,
+    T::Err: std::fmt::Debug,
+{
+    tokens.next()?.parse::<T>().ok()
+}
+
+fn main() {
+    let mut input_buf = String::new();
+    io::stdin().read_to_string(&mut input_buf).unwrap();
+    let mut input = input_buf.split_whitespace();
+
+    let s: String = read_value(&mut input).unwrap();
+
+    if s.len() % 5 == 0 {
+        print!("Yes");
+    } else {
+        print!("No");
+    }
+}
diff --git a/ABC451/oni0nfr1/B.rs b/ABC451/oni0nfr1/B.rs
new file mode 100644
index 0000000..c2e74ba
--- /dev/null
+++ b/ABC451/oni0nfr1/B.rs
@@ -0,0 +1,35 @@
+use std::{
+    io::{self, Read},
+    str::{FromStr, SplitWhitespace},
+};
+
+fn read_value<T>(tokens: &mut SplitWhitespace<'_>) -> Option<T>
+where
+    T: FromStr,
+    T::Err: std::fmt::Debug,
+{
+    tokens.next()?.parse::<T>().ok()
+}
+
+fn main() {
+    let mut input_buf = String::new();
+    io::stdin().read_to_string(&mut input_buf).unwrap();
+    let mut input = input_buf.split_whitespace();
+
+    let n: usize = read_value(&mut input).unwrap();
+    let m: usize = read_value(&mut input).unwrap();
+
+    let mut result = vec![0; m];
+
+    for _ in 0..n {
+        let a: usize = read_value::<usize>(&mut input).unwrap() - 1;
+        let b: usize = read_value::<usize>(&mut input).unwrap() - 1;
+
+        result[a] -= 1;
+        result[b] += 1;
+    }
+
+    for idx in 0..m {
+        println!("{}", result[idx]);
+    }
+}
diff --git a/ABC451/oni0nfr1/C.rs b/ABC451/oni0nfr1/C.rs
new file mode 100644
index 0000000..c3532c5
--- /dev/null
+++ b/ABC451/oni0nfr1/C.rs
@@ -0,0 +1,132 @@
+use std::{
+    io::{self, Read},
+    str::{FromStr, SplitWhitespace},
+    fmt::Write,
+};
+
+fn read_value<T>(tokens: &mut SplitWhitespace<'_>) -> Option<T>
+where
+    T: FromStr,
+    T::Err: std::fmt::Debug,
+{
+    tokens.next()?.parse::<T>().ok()
+}
+
+struct Node {
+    value: i32,
+    count: usize,
+    left: Option<Box<Node>>,
+    right: Option<Box<Node>>,
+}
+
+impl Node {
+    fn new(value: i32) -> Self {
+        Node {
+            value,
+            count: 1,
+            left: None,
+            right: None,
+        }
+    }
+
+    fn append(&mut self, value: i32) {
+        if self.value < value {
+            if let Some(right) = &mut self.right {
+                right.append(value);
+            } else {
+                // 실수 (오타)
+                // self.right = Some(Box::new(Node::new(value)));
+                self.left = Some(Box::new(Node::new(value)));
+            }
+        } else if self.value > value {
+            if let Some(left) = &mut self.left {
+                left.append(value);
+            } else {
+                self.left = Some(Box::new(Node::new(value)));
+            }
+        }
+
+        self.count += 1;
+    }
+
+    fn extract_left(&mut self) -> Option<Box<Self>> {
+        if let Some(extracted) = self.left.take() {
+            self.count -= extracted.count;
+            self.left = None;
+            return Some(extracted);
+        } else {
+            return None;
+        }
+    }
+
+    fn cut(mut self, value: i32) -> Option<Box<Self>> {
+        // 루트가 value보다 작으면 자신은 버리고, 자신의 오른쪽을 cut한 값을 반환 (재귀)
+        // 오른쪽이 비어 있으면?
+        // None 반환
+
+        // 루트가 value와 같으면 자신은 버리고, 자신의 오른쪽을 반환 (재귀 끝)
+        // 오른쪽이 비어 있으면?
+        // None 반환
+
+        // 루트가 value보다 크면, 자신의 왼쪽을 cut하고(재귀) 그 결과를 루트에 다시 넣음, 루트를 반환
+        // 왼쪽이 비어 있으면?
+        // 그냥 자기 반환
+
+        if self.value < value {
+            return self.right?.cut(value);
+        } else if self.value > value {
+            if let Some(left) = self.extract_left() {
+                let left_result = left.cut(value);
+                // 버그: 왼쪽을 뗐다가 붙이면서 count 값을 다시 복구하지 않음
+                // if let Some(left_result_node) = &left_result {
+                //     self.count += left_result_node.count;
+                // }
+                self.left = left_result;
+                return Some(Box::new(self));
+            } else {
+                return Some(Box::new(self));
+            }
+        } else {
+            return self.right;
+        }
+    }
+}
+
+fn main() {
+    let mut input_buf = String::new();
+    io::stdin().read_to_string(&mut input_buf).unwrap();
+    let mut input = input_buf.split_whitespace();
+    let mut output = String::new();
+
+    let q: usize = read_value(&mut input).unwrap();
+    let mut root: Option<Box<Node>> = None;
+
+    for _ in 0..q {
+        let cmd: u8 = read_value(&mut input).unwrap();
+        let h: i32 = read_value(&mut input).unwrap();
+
+        if cmd == 1 {
+            if let Some(mut root_some) = root.take() {
+                root_some.append(h);
+                root = Some(root_some);
+            } else {
+                root = Some(Box::new(Node::new(h)));
+            }
+        } else if cmd == 2 {
+            if let Some(root_some) = root.take() {
+                root = root_some.cut(h);
+            }
+        }
+
+        // 디버그용
+        println!("{}", root.is_none());
+
+        if let Some(root_some) = &root {
+            writeln!(output, "{}", root_some.count).unwrap();
+        } else {
+            writeln!(output, "0").unwrap();
+        }
+    }
+
+    print!("{output}");
+}
\ No newline at end of file