
#include <bits/stdc++.h>
using namespace std;
#define bolt                 \
    ios::sync_with_stdio(0); \
    cin.tie(0);              \
    cout.tie(0)
#define test   \
    int tt;    \
    cin >> tt; \
    while (tt--)
#define ll long long
#define ld long double
#define vi vector<ll>
#define pb push_back
#define F first
#define S second
#define mod 1000000007
#define all(v) v.begin(), v.end()
#define allr(v) v.rbegin(), v.rend()
int main(){
    bolt;
    ll a,b,c,d;cin>>a>>b>>c>>d;
    if(d>=a*b && d<=a*c){
        cout<<"No"<<endl;
    }else{
        cout<<"Yes"<<endl;
    }
}
#include <iostream>
using namespace std;
int main(void)
{
    double v, t, s, d;
    cin >> v >> t >> s >> d;
    if(d/v-s > 1e-7 || 1e-7 < t-d/v) cout << "Yes" << endl;
    else cout << "No" << endl;
    return 0;
}