#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 + i)))
        {
            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;
}