#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<math.h>

int main(){
  int a,b,c,d;
  int flag = 0;

  scanf("%d %d %d %d", &a, &b, &c, &d);

  do{
    if(c <= b){
      flag = 1;
      break;
    }

    else c -= b;

    if(a <= d){
      flag = -1;
      break;
    }

    else a -= d;
  }while(a > 0 && c > 0);

  if(flag == 1) printf("Yes\n");

  else if(flag == -1) printf("No\n");
  return 0;
}
