#include<bits/stdc++.h>
#define re register
using namespace std;
inline int read(){
	re int t=0;re char v=getchar();
	while(v<'0')v=getchar();
	while(v>='0')t=(t<<3)+(t<<1)+v-48,v=getchar();
	return t;
}
int a,b,c,d;
int main(){
	a=read();b=read();c=read();d=read();
	b=(c-1)/b+1;d=(a-1)/d+1;
	if(b<=d)puts("Yes");
	else puts("No");
}