#include <stdio.h>
#include<ctype.h>
int main() {
    int N;
    scanf("%d",&N);
    if(N<=0 || N> 100)
    {
        printf("Invalid input");
        return 0;
    } 
    char arr[N];
    for(int i=0; i<N;i++)
    {
        scanf(" %c",&arr[i]);
    }
    int evenSum = 0,oddSum =0;
    char *ptr = arr;
    for(int i =0;i<N;i++)
    {
        if(!isalpha(*(ptr + 1)))
        {
            printf("Invalid input");
        return 0;
        }
        if(*(ptr + i) %2==0)
        evenSum +=(ptr +i);
        else
        oddSum +=*(ptr  = i);
    }
    int diff = evenSum - oddSum;
    if(diff < 0) diff = -diff;
    printf("%d",diff);
    return 0;
}