#include<stdio.h>
#include<ctype.h>
int main() {
    int N;
    scanf("%d",&N);
    if(N <= 0) {
        printf("-1");
        return 0;
    }
    int ascii = (int)ch;
    if(ascii % 2 == 0) {
        evenSum +=ascii;
        
    }
    else {
        oddSum += ascii;
    }
    printf("%d",oddSum-evenSum);
    return 0;
}