#include<stdio.h>

int main(void){
  int a,b,c,d,turn=0;
  
  scanf("%d %d %d %d",&a,&b,&c,&d);
  
  while(a>0 && c>0){
    if(turn%2==0){
      c -= b;
    }
    else{
      a -= d;
    }
    turn++
  }
  
  if(a>0)
    printf("Yes");
  else
    printf("No");
  
  return 0;
}