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,布布扣,bubuko.com
Codeforces Testing Round #10 A. Forgotten Episode
原文：http://www.cnblogs.com/xiongqiangcs/p/3778919.html