#iclude<stdio.h>
#include<ctype.k>
int main()
{
    int N;
    scanf("%d", &N);
    if(N<0)
    {
        printf("Invalid input");
        return 0;
    }
    char arr[101];
    int sumEven = 0,sumOdd = 0;
    for(int i = 0;i<N;i++)
    {
        scanf("%c", &arr[i]);
        if(!isalpha(arr[i]))
        {
            printf("Invalid input");
            return 0;
        }
        int ascii = *(arr +i);
        if(ascii %2 ==0)
        sumEven +=ascii;
        else
        sumOdd += ascii;
    }
    int difference = sumEven - sumOdd;
    printf("%d",difference);
    return 0;
}