#include<iostream>
#include<string>
#include<algorithm>
#include<bits/stdc++.h>
#include<iomanip>
using namespace std;

typedef long long ll;
typedef long double ld;

int MOD=1000000007;


int main(){
    ll A,B,C,D;
    cin >> A >> B >> C >> D;
    while(1){
        C=C-B;
        if(C<=0){cout << "Yes" << endl; return 0;}
        A=A-D;
        if(A<=0){cout << "No" << endl; return 0;}
    }
    }