#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1LL << 60;

int main() {
    int A, B, C, D;
    cin >> A >> B >> C >> D;
    bool t = false;
    while (true) {
        C -= B;
        if (C <= 0) {
            t = true;
            break;
        }
        A -= D;
        if (A <= 0) {
            break;
        }
    }

    if (t) {
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }
}