#include<stdio.h>

int main(void){
  int s = 0;
  int w = 0;
  int x = 0;
  int y = 0;
  scanf("%d", &s);
  scanf("%d", &w);
  scanf("%d", &x);
  scanf("%d", &y);
  int e = s/y;
  int f = s%y;
  int g = x/w;
  int h = x%y;
  while(1){
  	x = x-w;
  	if(x<=0){
  		printf("Yes");
  		break;
  	}
  	s = s-y;
  	if(s<=0){
  		printf("No");
  		break;
  	}
  }
}