#include<bits/stdc++.h>

using namespace std;

int main()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	
	int h1, s1, h2, s2;
	cin >> h1 >> s1 >> h2 >> s2;
	while(h1 > 0 and h2 > 0){
		h2 -= s1;
		if(h2 > 0) h1 -= s2;
		else break;
	}
	if(h1 > 0) cout << "Yes";
	else cout << "No";

	return 0;
}

