#include <bits/stdc++.h>

using namespace std;

int main() {
    int v, t, s, d;
    cin >> v >> t >> s >> d;
    if (v * t <= d && d <= v * s) {
        cout << "No" << endl;
    } else {
        cout << "Yes" << endl;
    }
    return 0;
}

#include <iostream>
#include <bits/stdc++.h>
#include <cstdio>
#include <stack>
#include<algorithm>
using namespace std;

int main() {
	int X, Y;
	cin >> X >> Y;
	if (max(X, Y) < min(X, Y) + 3) {
		cout << "Yes" << endl;
	}
	else {
		cout << "No" << endl;
	}
}
