Codeforces Testing Round #10 A. Forgotten Episode

水题，注意数据范围

#include <iostream>

using namespace std;

int main(){

    long long n,a;

    cin >> n;

    long long  sum =(n*(n+1))>>1;

    for(int i = 0 ; i < n-1 ; ++i){

        cin >>a;

        sum -=a;

    }

    cout<<sum<<endl;

}

Codeforces Testing Round #10 A. Forgotten Episode