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

int calculate_ascii_sum(char *initials, int n) {
    int sum = 0;
    for (int i = 0; i < n;i++) {
        if (!isalpha(*ptr)) {
            return -1;
        }
        sum +=*ptr;
        ptr++;
    }
    return sum;
}
int main(){
    int n;
    scanf("%d", &n);
    
    char initials[n];
    for (int i = 0; i < n; i++) {
        scanf("%c", &initials[i]);
    }
    
    int sum = calculate_ascii_sum(initials, n);
    printf("%d\n", sum);
    return 0;
}