OJ Board

hi
i'm new to programming contest.
what's wrong with my code:

#include<stdio.h>
#include<stdlib.h>
int main()
{
long long int num1;
long long int num2;
while(scanf("%lld %lld",&num1,&num2) !=EOF)
printf("%lld\n",abs(num2-num1));
return 0;
}

the UVA's gcc returns wrong answer.