#include<stdio.h>

int main(){
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  while(a > 0 && c > 0){
    c -= b;
    a -= d;
  }
  if(a > 0) printf("Yes");
  else if(c <= 0) printf("Yes");
  if(c > 0) printf("No");
}