#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
int main()
{
    int N;
    scanf("%d",&N);
    if(N < 0)
    {
        printf("Invalid input");
        return 0;
    }
    char arr[200];
    char *ptr=arr;
    for(int i=0;i<N;i++)
    {
        scanf( "%c",arr[i]);
        if(!isalpha(*(ptr +i)))
        {
            printf("Invalid input");
            return 0;
        }
    }
    int evensum=0,oddsum=0;
    for(int i=0;i<N;i++)
    {
        int ascii=arr[i];
        if(ascii%2==0)
        evensum += ascii;
        else
        oddsum += ascii;
        int diff = oddsum-evensum;
        printf("%d\n",diff);
        return 0;
    }
}