What's wrong with my code?


#include <stdio.h>
#include <math.h>

double t11, t12, t21, t22;
double h11, h12, h21, h22;
double t1, t2, lb, rb, t, h;

int main () {
 scanf ("%lf%lf", &t11, &t12);
 scanf ("%lf%lf", &t21, &t22);
 h11 = floor (t11);
 h12 = floor (t12);
 h21 = floor (t21);
 h22 = floor (t22);
 if ((h11 > 17) && (h12 < 7)) {
  h12 += 24;
  t12 += 24;
 }
 if ((h21 > 17) && (h22 < 7)) {
  h22 += 24;
  t22 += 24;
 }
 t1 = (h12 - h11) + (t12 - h12 - t11 + h11) / 60;
 t2 = (h22 - h21) + (t22 - h22 - t21 + h21) / 60;
 t = (t1 - t2) / 2;
 lb = t - 1. / 12 + 1e-20;
 rb = t + 1. / 12 - 1e-20;
 printf ("%.0lf\n", fabs (ceil(lb)));
 return 0;
}