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

int main(){
    int A, B, C, D;
    cin >> A >> B >> C >> D;
    while(A>0||B>0){
        C -= B;
        if(C<=0){
            cout << "Yes" << endl;
            return 0;
        }
        A -= D;
        if(A<=0){
            cout << "No" << endl;
            return 0;
        }
    }
    return 0;
 }
