diff --git a/ABC451/mshuun/A_illegal.py b/ABC451/mshuun/A_illegal.py
new file mode 100644
index 0000000..988fc29
--- /dev/null
+++ b/ABC451/mshuun/A_illegal.py
@@ -0,0 +1 @@
+print("Yes"if len(input())%5==0 else"No")
\ No newline at end of file
diff --git a/ABC451/mshuun/B_Personnel_Change.py b/ABC451/mshuun/B_Personnel_Change.py
new file mode 100644
index 0000000..8b5d693
--- /dev/null
+++ b/ABC451/mshuun/B_Personnel_Change.py
@@ -0,0 +1,9 @@
+N, M = map(int, input().split())
+A = [0] * M
+
+for _ in range(N):
+    a, b = map(int, input().split())
+    A[a-1] -= 1
+    A[b-1] += 1
+
+print(*A, sep="\n")
\ No newline at end of file
diff --git a/ABC451/mshuun/C_Understory.py b/ABC451/mshuun/C_Understory.py
new file mode 100644
index 0000000..bafe28c
--- /dev/null
+++ b/ABC451/mshuun/C_Understory.py
@@ -0,0 +1,12 @@
+import sys
+from heapq import *
+input = sys.stdin.readline
+T = []
+for _ in range(int(input())):
+    c, h = map(int, input().split())
+    if c == 1:
+        heappush(T, h)
+    else:
+        while T and T[0] <= h:
+            heappop(T)
+    print(len(T))
diff --git a/ABC451/mshuun/D_Concat_Power_of_2.py b/ABC451/mshuun/D_Concat_Power_of_2.py
new file mode 100644
index 0000000..20c8810
--- /dev/null
+++ b/ABC451/mshuun/D_Concat_Power_of_2.py
@@ -0,0 +1,17 @@
+N = int(input())
+ns = [set() for _ in range(10)] 
+
+for i in range(30):
+    n = 2**i
+    ns[len(str(n))].add(n)
+
+for tar in range(2, 10):
+    for cur in range(1, tar // 2 + 1):
+        for a in ns[cur]:
+            for b in ns[tar - cur]:
+                ns[tar].add(int(str(a) + str(b)))
+                ns[tar].add(int(str(b) + str(a)))
+
+
+ans = sorted(set().union(*ns))
+print(ans[N - 1])
\ No newline at end of file