#include <stdio.h>

int main(void)
{
  int a,b,c,d;
  int damage_T=0;
  int damage_A=0;
  scanf("%d %d %d %d", &a, &b, &c, &d);
  for(int i=1;i<1000;i++){
    damage_A += b;
    if(damage_A >= c){
      printf("Yes\n");
      break;
    }
    damage_T += d;
    if(damage_T >= a){
      printf("No\n");
      break;
    }
  }
  return 0;
}
