// problem-type?
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

void solve(){
    int h1, s1, h2, s2;
    cin >> h1 >> s1 >> h2 >> s2;
    int turns1 = (int)ceil((double)h2/s1);
    int turns2 = (int)ceil((double)h1/s2);
    if(turns1 <= turns2) cout << "yes";
    else cout << "no";
}

int main(){
    cin.tie(0);
    ios_base::sync_with_stdio(0);
    int t = 1;
    //cin >> t;
    while(t--){
        solve();
        cout << '\n';
    }
}