#include <bits/stdc++.h>
using namespace std;
long long ans = 0;
string str;
int n;
int main() {
  ios::sync_with_stdio(false);
  cin >> n;
  cin >> str;
  for (int i = 0; i < n; ++i) ans += (str[i] - '0') & 1 ? 0 : i + 1;
  cout << ans << endl;
  return 0;
}
