#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>

int calculateBalance(char *str, int N){
    int evensum = 0, oddsum = 0;
    for(int i = 0; i < N; i++){
        if(!isalpha(*(str + i))){
            printf("Invalid input");
            exit(0);
        }
        int ascii = (int)*(str + i);
        if (ascii % 2 == 0){
            evensum += ascii;
        } else{
            oddsum += ascii;
        }
    }
    return abs(evensum - oddsum);
}

int main(){
    int N;
    scanf("%d", &N);
    
    if(N < 0){
        printf("Invalid input\n");
        return 0;
    }
    char *initials = (char *)malloc(N + 1) * sizeof(char));
    scanf("%s",initials);
    
    int result = calculateBalance(initials, N);
    printf("%d\n", result);
    
    free(initials);
    return 0;
}