#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int sum = 0, mul, n, in, count = 1;
  cin >> n;
  while (n > 1) {
    cin >> in;
    mul = count * (in - 1);
    sum += mul;
    count++;
    n--;
  }
  if (n > 0) {
    cin >> in;
    mul = count * (in);
    sum += mul;
    cout << sum << endl;
  } else
    cout << sum << endl;
  return 0;
}
