void is_reachable(int a, int b, int speed, int time_limit) {
   int result;
   int dist;
   if (a <= b) {
     dist = (b - a);
   } else {
     dist = (a - b);
   };
   if (dist <= (time_limit * speed)) {
     result = 1;
   } else {
     result = 0;
   };

 }