#include <iostream>
#include <cmath>
using namespace std;

bool isAlpha(char c) {
    return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
}

int main() {
    int n;
    cin >> n;

    if (n <= 0 || n > 100) {
        cout << "Invalid input";
        return 0;
    }

    char arr[100];
    for (int i = 0; i < n; i++) {
        cin >> arr[i];
        if (!isAlpha(arr[i])) {
            cout << "Invalid input";
            return 0;
        }
    }

    int evenSum = 0, oddSum = 0;
    char *ptr = arr;
    for (int i = 0; i < n; i++, ptr++) {
        if (i % 2 == 0)
            evenSum += int(*ptr);
        else
            oddSum += int(*ptr);
    }

    cout << abs(evenSum - oddSum);
    return 0;
}