#include<stdio.h>
#include<ctype.h>
#include<stdlib.h>
int main()
{
    int N;
    scanf("%d" , &N);
    if(N<=0){
        printf("Invalid input");
        return 0;
    }
    char ch;
    int even_sum=0,odd_sum=0;
    for(int i=0;i<N;i++){
        scanf(" %c" ,&ch);
        if(!isalpha(ch)){
            printf("Invalid input");
            return 0;
        }
        int *ptr = (int*)&ch;
        if(i%2==0)
        even_sum+=*ptr;
        else
        odd_sum+=*ptr;
    }
    int diff =abs(even_sum-odd_sum);
    printf("%")
}