#include <bits/stdc++.h>
using namespace std;
int main() {
int S1, V1, S2, V2;
cin >> S1 >> V1 >> S2 >> V2;
if ((double)S1 / V1 < (double)S2 / V2) {
cout << "YES" << endl;
} else {
cout << "NO" << endl;
}
return 0;
}
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