#include<stdio.h>
#include<ctype.h>
int main() {
    int N;
    scanf("%d",&N);
    if(N <= 0)
    {
        printf("-1");
        return 0;
    }
    char ch;
    int oddsum=0,evensum=0;
    for(int i =0; i< N; i++)
    {
        scanf("%c",&ch);
        if(isalpha)
    
    int ascii = (int)ch;
    if(ascii % 2 == 0)
    {
        evensum +=ascii;
    }
    else 
    (oddsum-evensum);
        return 0;
    }