#include <stdio.h>
int main(void){
  int Ht,Ha,At,Aa;
  int i=0;
  scanf("%d",&Ht);
  scanf("%d",&Ha);
  scanf("%d",&At);
  scanf("%d",&Aa);
  while(Ht>0){
    Ha-=At;
    if(Ha<=0){ 
      break;
      i=1;
    }
    Ht-=Aa;
  }
  if(i==1) printf("Yes");
  if(i==0) printf("No");
  return 0;
}