#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int sum = 0, n, p;
  vector<long long int> v;
  long long int c;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> c;
    v.push_back(c);
  }
  for (int i = 0; i < n; i++) {
    p = v[i];
    sum = sum + p + p * i - i;
  }
  cout << sum;
  return 0;
}
