#include<stdio.h>
int main(void){
  int A,B,C,D;
  scanf("%d %d %d %d ",&A,&B,&C,&D);
  while(1){
    C= C-B;
    if(C<=0){
      printf("Yes");
      break;
    }
    A = A-D;
    if(A<=0){
      printf("No");
      break;
    }
  }
}