#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<ll, ll>;
using vll = vector<ll>;
using vvll = vector<vector<ll>>;
const ll INF = 1e18;
#define pu push
#define pb push_back
#define mp make_pair
#define print(x) cout << (x) << endl;
#define rep(i,n) for(ll i = 0; i < (n); i++)
#define SORT(x) sort(x.begin(),x.end())
#define POSL(x,v) (lower_bound(x.begin(),x.end(),v)-x.begin())
#define POSU(x,v) (upper_bound(x.begin(),x.end(),v)-x.begin())
#define fi first
#define sc second

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    //cout << fixed << setprecision(10);
    int A, B, C, D;
    cin >> A >> B >> C >> D;
    if ((D-1)/A >= (C-1)/B) {
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }
}