#include <stdio.h>

int main(){
  int a,b,c,d;

  scanf("%d %d %d %d",&a,&b,&c,&d);
  
  while(1){
    c -= b;
    if(c <= 0){
      printf("Yes\n");
      break;
    }
    a -= d;
    if(a <= 0){
      printf("No\n");
      break;
    }
  }

  return 0;
}
