#include<bits/stdc++.h>
using namespace std;

int main()
{
  int N;
  cin >> N;
  int ret = 0;
  for(int i = 0; i <= N; i++) {
    int a;
    cin >> a;
    if(i == N) a = -a;
    ret += a;
  }
  cout << ret << endl;
}