#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int n;
  cin >> n;
  long long int sol = 0, x;
  for (long long int i = 1; i <= n; i++) {
    cin >> x;
    if (i == 1)
      sol = x;
    else
      sol = sol + i * x - i + 1;
  }
  cout << sol << endl;
  return 0;
}
