#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define rep(i,n) for (int i=0;i < n; ++i)
using namespace std;
const int INF = 2147483647;
using ll = long long;


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int a,b,c,d;
    cin >> a >> b >> c >> d;
    while(1){
        c-=b;
        if(c<=0){
            cout << "Yes" << endl;
            return 0;
        }
        a-=d;
        if(a<=0){
            cout << "No" << endl;
            return 0;
        }
    }
    return 0;
}

