diff --git a/ABC451/sevenbellaa/A.cpp b/ABC451/sevenbellaa/A.cpp
new file mode 100644
index 0000000..d9a0b7f
--- /dev/null
+++ b/ABC451/sevenbellaa/A.cpp
@@ -0,0 +1,14 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int main() {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+
+  string s;
+  cin >> s;
+  if (s.length() % 5)
+    cout << "No";
+  else
+    cout << "Yes";
+}
\ No newline at end of file
diff --git a/ABC451/sevenbellaa/B.cpp b/ABC451/sevenbellaa/B.cpp
new file mode 100644
index 0000000..07e258c
--- /dev/null
+++ b/ABC451/sevenbellaa/B.cpp
@@ -0,0 +1,21 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int cur[101], nxt[101];
+
+int main() {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+  int N, M;
+  cin >> N >> M;
+  for (int i = 0; i < N; i++) {
+    int a, b;
+    cin >> a >> b;
+    cur[a]++;
+    nxt[b]++;
+  }
+
+  for (int i = 1; i <= M; i++) {
+    cout << nxt[i] - cur[i] << '\n';
+  }
+}
\ No newline at end of file
diff --git a/ABC451/sevenbellaa/C.cpp b/ABC451/sevenbellaa/C.cpp
new file mode 100644
index 0000000..06290be
--- /dev/null
+++ b/ABC451/sevenbellaa/C.cpp
@@ -0,0 +1,23 @@
+#include <bits/stdc++.h>
+
+#include <queue>
+using namespace std;
+
+int main() {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+
+  priority_queue<int, vector<int>, greater<>> pq;
+  int q;
+  cin >> q;
+  while (q--) {
+    int op, h;
+    cin >> op >> h;
+    if (op == 1) {
+      pq.push(h);
+    } else {
+      while (!pq.empty() && pq.top() <= h) pq.pop();
+    }
+    cout << pq.size() << '\n';
+  }
+}
\ No newline at end of file
diff --git a/ABC451/sevenbellaa/D.cpp b/ABC451/sevenbellaa/D.cpp
new file mode 100644
index 0000000..089fb86
--- /dev/null
+++ b/ABC451/sevenbellaa/D.cpp
@@ -0,0 +1,37 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+long long concat(long long a, long long b) {
+  long long tmp = b, cnt = 0;
+  while (tmp > 0) {
+    tmp /= 10;
+    cnt++;
+  }
+  return a * pow(10, cnt) + b;
+}
+
+vector<int> part;
+
+void make_num(long long prev) {
+  for (int i = 0; i < 30; i++) {
+    long long nx = concat(prev, part[i]);
+    if (nx <= (int)1e9) {
+      part.push_back(nx);
+      make_num(nx);
+    }
+  }
+}
+
+int main() {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+  for (int i = 0; i < 30; i++) part.push_back(1 << i);
+  for (int i = 0; i < 30; i++) make_num(part[i]);
+
+  sort(part.begin(), part.end());
+  part.erase(unique(part.begin(), part.end()), part.end());
+
+  int idx;
+  cin >> idx;
+  cout << part[idx - 1];
+}
\ No newline at end of file
diff --git a/ABC451/sevenbellaa/E_WA.cpp b/ABC451/sevenbellaa/E_WA.cpp
new file mode 100644
index 0000000..58cf24a
--- /dev/null
+++ b/ABC451/sevenbellaa/E_WA.cpp
@@ -0,0 +1,30 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int N, dist[3003][3003];
+
+int main() {
+  ios::sync_with_stdio(false);
+  cin.tie(nullptr);
+
+  cin >> N;
+  for (int i = 1; i < N; i++) {
+    for (int j = i + 1; j <= N; j++) cin >> dist[i][j];
+  }
+
+  for (int i = 1; i < N; i++) {
+    for (int j = i + 1; j <= N; j++) {
+      bool flag = false;
+      for (int k = i + 1; k < j; k++) {
+        if (dist[i][k] + dist[k][j] == dist[i][j]) flag = true;
+      }
+      if (!flag && j - i > 1) {
+        cout << i << j;
+        cout << "No";
+        return 0;
+      }
+    }
+  }
+
+  cout << "Yes";
+}
\ No newline at end of file