#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
constexpr int Inf = 1000000000;
constexpr ll INF= 9 * 1e18;
constexpr ll MOD = 1000000007;
const double PI = 3.1415926535897;
typedef pair<int,int> P;

template<typename T>
T Pow(T a,T b) {
    T ret = 1;
    for(int i = 0;i < b;i++) {
        ret *= a;
    }
    return ret;
}

ll mod(ll val) {
    ll res = val % MOD;
    if(res < 0) {
        res += MOD;
    }
    return res;
}

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;
        }
    }
}