#include <cstdio>
#include <cstring>
#include <cmath>
#include <utility>
#include <iostream>
#include <functional>
#include <bitset>
#include <algorithm>
#include <vector>
#include <forward_list>
#include <set>
#include <map>
#include <queue>
#include <deque>
#include <stack>
#include <numeric>
#define ll long long int
#define rep(i,n) for(int i=0;i<(n);i++)
using namespace std;

int main(){
    int l,r,m,k; 
    cin >> l >> r >> m >> k;
    if(k==0){
        cout << "Yes" << endl;
        return 0;
    }
    if(m / k <= r ){
        cout << "Yes" << endl;
        return 0;
    }
    
    cout << "No" << endl;
}