#include <stdio.h>

int main(){
  int hpT, atT, hpA, atA;
  scanf("%d%d%d%d", &hpT, &atT, &hpA, &atA);
  while(1){
    hpA -= atT;
    if(hpA <= 0){
      printf("Yes\n");
      break;
    }
    hpT -= atA;
    if(hpT <= 0){
      printf("No\n");
      break;
    }
  }
  return 0;
}
