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

int main(){
    int A,B,C,D;
    cin >> A >> B >> C >> D;
    int E = (C + B - 1) / B,F = (D + A - 1) / D;
    if (E > F){
        cout << "No" << endl;
    }
    else {
        cout << "Yes" << endl;
    }
}
