#include <iostream>
using namespace std;
long long n, t, tong;
int main() 
{
    cin >> n;
    for(int a = 0; a < n; a++)
    {
        cin >> t;
        if(a % 2 == 0) tong += t;
        else tong -= t;
    }
    cout << tong;
    return 0;
}

$#khanhtaon$

#include <bits/stdc++.h>

using namespace std;

#define int long long

int a[1000005], n, s = 0, s1 = 0;
main() {
  //freopen(".inp", "r", stdin);
  //freopen(".out", "w", stdout);
  ios_base::sync_with_stdio(0);
  cin.tie(nullptr);
  cin >> n;
  for (int i = 1; i <= n; ++i)
  {
    cin >> a[i];
    if (i % 2 == 0) s += a[i];
    else s1 += a[i];
  }
  cout << s1 - s;
  return 0;
}