#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#define ll long long
using namespace std;

const ll mod = 1e9 + 7;

ll C[2005][2005];
ll dp[100005][13];


int main(){
    int A,B,C,D,ans;
    cin >> A >> B >> C >> D;
    if(C / B >= A / D){
        cout << "Yes" << endl;
    }else{
        cout << "No" << endl;
    }
}