#include<stdio.h>
int main(){
  int a,b,c,d;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  while(a > 0 && c > 0){
  	if(0 >= (c = c - b)){
    	printf("Yes\n");
        return 0;    
    }
    if(0 >= (a = a - d)){
    	printf("No\n");
  		return 0;    
    }
  }
}