#include <bits/stdc++.h>
using namespace std;
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, -1, 0, 1};
int main() {
  long long n;
  cin >> n;
  long long a[n];
  long long sum = 1;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    sum *= a[i];
  }
  cout << sum - 1 << endl;
}
