請問為什麼這樣會預時?

我原本用int沒預時阿!

#include <stdio.h>

int main()
{
  long int a,b,n;
    while (scanf("%l %l",&a,&b)!=-1){

           a= a + a%2;
           b= b - b%2;
           n=(b/2)-(a/2)+1;
           printf("%l\n",n);
           }
           
  return 0;
}