#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 es=0,os=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)
    es+= *(ptr+i);
    else
    os += *(ptr+i);
}
int diff=es-es;
if(diff<0) diff=- diff;
printf("%d",diff);
return 0;
}