#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <iostream>
#include <string>
#include <map>
#include <queue>
#include <stdio.h>
#include <math.h>

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

typedef vector<vector<int>> vvi;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vector<string>> vvs;
typedef vector<ll> vll;

typedef pair<int, int> pii;

typedef queue<int> qi;
typedef queue<string> qs;


#define rep(i, n) for(int i=0; i<(n); ++i)
#define repp(i, a, b) for(int i = (a); i <= (b); i++)
#define repm(i, a, b) for(int i = (a); i >= (b); i--)

#define all(v) v.begin(), v.end()
//sort( all(v) )　などと使える

int main(){
    int a, b, c, d;
    cin >> a >> b >> c >> d;

    int n = (c + b-1)/b;
    int m = (a + d-1)/d;

    if(n <= m) cout << "Yes" << endl;
    else cout << "No" << endl;
}