548A

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int n;
    cin >> n;
    unsigned long result = 0;
    string s;
    cin >> s;
    for(int i = 0; i < s.length(); i++)
        {
            string temp (&s.at(i), sizeof(char));
            if(stoi(temp) % 2 == 0)
            {
                result += i + 1;
            }
        }
    cout << result;
    return 0;
}