#include <stdio.h>

int main(){
  int A,B,C,D;
  scanf("%d %d %d %d",&A,&B,&C,&D);
  
  while(1){
	C = C - B;
    if(0 >= C){
	  printf("Yes\n");
      break;
    }
    A = A - D;
    if(0 >= A){
	  printf("No\n");
      break;
    }
  }
  
  return 0;
}