diff --git a/ABC451/dib3474/A.cpp b/ABC451/dib3474/A.cpp
new file mode 100644
index 0000000..b14062e
--- /dev/null
+++ b/ABC451/dib3474/A.cpp
@@ -0,0 +1,13 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int main() {
+    string s;
+    cin >> s;
+    if (s.size() % 5 == 0) {
+        cout << "Yes" << '\n';
+    }
+    else {
+        cout << "No" << '\n';
+    }
+}
\ No newline at end of file
diff --git a/ABC451/dib3474/B.cpp b/ABC451/dib3474/B.cpp
new file mode 100644
index 0000000..ceebcef
--- /dev/null
+++ b/ABC451/dib3474/B.cpp
@@ -0,0 +1,24 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+vector<int> before, after;
+
+int main() {
+    int n, m;
+    cin >> n >> m;
+
+    before.assign(m + 1, 0);
+    after.assign(m + 1, 0);
+
+    for (int i = 0; i < n; i++) {
+        int b, a;
+        cin >> b >> a;
+
+        before[b]++;
+        after[a]++;
+    }
+
+    for (int i = 1; i <= m; i++) {
+        cout << after[i] - before[i] << '\n';
+    }
+}
\ No newline at end of file
diff --git a/ABC451/dib3474/C.cpp b/ABC451/dib3474/C.cpp
new file mode 100644
index 0000000..47fac8b
--- /dev/null
+++ b/ABC451/dib3474/C.cpp
@@ -0,0 +1,25 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+priority_queue<int, vector<int>, greater<int>> trees;
+
+int main() {
+    cin.tie(0)->sync_with_stdio(0);
+
+    int Q;
+    cin >> Q;
+    while (Q--) {
+        int q, h;
+        cin >> q >> h;
+        if (q == 1) {
+            trees.push(h);
+            cout << trees.size() << '\n';
+        }
+        else if (q == 2) {
+            while (!trees.empty() && trees.top() <= h) {
+                trees.pop();
+            }
+            cout << trees.size() << '\n';
+        }
+    }
+}
\ No newline at end of file
diff --git a/ABC451/dib3474/E.cpp b/ABC451/dib3474/E.cpp
new file mode 100644
index 0000000..3fdcf28
--- /dev/null
+++ b/ABC451/dib3474/E.cpp
@@ -0,0 +1,87 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+vector<vector<pair<int, int>>> graph;
+vector<vector<int>> board;
+vector<vector<int>> costs;
+
+struct node {
+    int a;
+    int b;
+    int w;
+};
+
+struct Compare {
+    bool operator()(const node& i, const node& j) {
+        return i.w > j.w;
+    }
+};
+
+priority_queue<node, vector<node>, Compare> pq;
+
+vector<int> parent;
+
+int find(int e) {
+    if (parent[e] == e) return e;
+    else {
+        return parent[e] = find(parent[e]);
+    }
+}
+
+int n;
+
+void dfs(int start, int curr, int prev, int total_dist) {
+    costs[start][curr] = total_dist;
+    for (auto& [next_node, weight] : graph[curr]) {
+        if (next_node != prev) {
+            dfs(start, next_node, curr, total_dist + weight);
+        }
+    }
+}
+
+int main() {
+    cin.tie(0)->sync_with_stdio(0);
+    cin >> n;
+    board.assign(n + 1, vector<int>(n + 1));
+    parent.assign(n + 1, 0);
+    for(int i=1; i<=n; i++) parent[i] = i;
+    graph.assign(n + 1, vector<pair<int, int>>());
+    costs.assign(n + 1, vector<int>(n + 1, 0));
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = i + 1; j <= n; j++) {
+            cin >> board[i][j];
+            pq.push({i, j, board[i][j]});
+        }
+    }
+
+    int edges = 0;
+    while(!pq.empty() && edges < n - 1) {
+        auto [a, b, w] = pq.top(); pq.pop();
+        if (find(a) != find(b)) {
+            parent[find(a)] = find(b);
+            graph[a].push_back({b, w});
+            graph[b].push_back({a, w});
+            edges++;
+        }
+    }
+
+    if (edges != n -1) {
+        cout << "No";
+        return 0;
+    }
+
+    for (int i = 1; i <= n; i++) {
+        dfs(i, i, -1, 0);
+    }
+
+    for (int i = 1; i <= n; i++) {
+        for (int j = i + 1; j <= n; j++) {
+            if (costs[i][j] != board[i][j]) {
+                cout << "No";
+                return 0;
+            }
+        }
+    }
+    cout << "Yes";
+}
\ No newline at end of file