#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
const ll mod = 1000000007;
const ll INF = mod * mod;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)

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