#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep1(i, n) for (int i = 1; i < (n); i++)
#define erep(i, n) for (int i = 0; i <= (n); i++)
#define erep1(i, n) for (int i = 1; i <= (n); i++)
using namespace std;
using ll = long long;

int main() {
    int thp, tatk, ahp, aatk;
    cin >> thp >> tatk >> ahp >> aatk;
    while (thp > 0 && ahp > 0) {
        ahp -= tatk;
        if (ahp <= 0) {
            cout << "Yes" << endl;
            break;
        }
        thp -= aatk;
        if (thp <= 0) {
            cout << "No" << endl;
            break;
        }
    }
    return 0;
}