diff --git a/AtCoder/ABC244/C/C.cpp b/AtCoder/ABC244/C/C.cpp
new file mode 100644
index 00000000..431d8984
--- /dev/null
+++ b/AtCoder/ABC244/C/C.cpp
@@ -0,0 +1,23 @@
+#include <iostream>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+const int N = 2005;
+
+int n, x;
+bool tag[N];
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin >> n;
+    do {
+        tag[x] = true;
+        int t = 0;
+        while (tag[++t] && t <= 2 * n + 1) {}
+        tag[t] = true;
+        cout << t << endl;
+    } while (cin >> x, x);
+    return 0;
+}