func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(0);     cout.tie(0);     cin.tie(0);     int64_t a, b;     cin >> a;     a = a * (a + 1) / 2;     while (cin >> b) a -= b;     cout << a;   }   