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

int main(){
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    int taka = (c + b - 1) / b;
    int aok = (a + d - 1) / d;
    string ans = "Yes";
    if(taka > aok) ans = "No";
    cout << ans << endl;
}