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