diff --git a/AtCoder/ABC220/B/B.cpp b/AtCoder/ABC220/B/B.cpp
new file mode 100644
index 00000000..adfb68b6
--- /dev/null
+++ b/AtCoder/ABC220/B/B.cpp
@@ -0,0 +1,51 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int k;
+long long aa, bb, x;
+string a, b;
+
+int ctoi(char c) {
+    int r;
+    switch (c) {
+        case 'A':
+            r = 10;
+            break;
+        case 'B':
+            r = 11;
+            break;
+        case 'C':
+            r = 12;
+            break;
+        case 'D':
+            r = 13;
+            break;
+        case 'E':
+            r = 14;
+            break;
+        case 'F':
+            r = 15;
+            break;
+        default:
+            r = c - '0';
+            break;
+    }
+    return r;
+}
+
+int main() {
+    cin >> k >> a >> b;
+    x = 1;
+    for (int i = a.size() - 1; i >= 0; i--) {
+        aa += ctoi(a[i]) * x;
+        x *= k;
+    }
+    x = 1;
+    for (int i = b.size() - 1; i >= 0; i--) {
+        bb += ctoi(b[i]) * x;
+        x *= k;
+    }
+    cout << aa * bb << endl;
+    return 0;
+}