#include <bits/stdc++.h>
using namespace std;

using ll= long long;
// #define double long double
#define sz(x) (int)x.size()
#define all(x) (x).begin(),(x).end()
#define IOS ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define _set(x) __builtin_popcount(x)
#define _setl(x) __builtin_popcountll(x)
#define PI  3.14159265358979323846264338327950L
#define mod 1000000007LL

#ifdef LOCAL
	#define elapsed_time      1.0 * clock() / CLOCKS_PER_SEC 
#endif

void debug(){
	cerr<<"]\n";
}
template<class H,class ... T> void debug(H h,T... t){
	cerr<<h;
	if(sizeof... (t)){
		cerr<<", ";
	}
	debug(t...);
}

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

#ifdef DEBUG
	#define dbg(...) cerr << "LINE(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", debug(__VA_ARGS__)
	#define dpv(...) cerr<< "["#__VA_ARGS__ " : ";for(int i: (__VA_ARGS__)){cerr<<i<<" ";}cerr<<"]\n"
#else
	#define dbg(...) 0
	#define dpv(...) 0
#endif

void solve(){
	int v, t,s ,d;
	cin>>v>>t>>s>>d;
	t *= v;
	s *= v;
	if(s< t) swap(s, t);
	if(!(d<= s && d>= t)){
		cout<<"Yes\n";
	}else{
		cout<<"No\n";
	}
}

int32_t main(){
	IOS
	// freopen("input.txt","r",stdin);
	int _;
	// cin>>_;
	_=1;
	for(int i=1;i<=_;i++){
		// cout<<"Case #"<<i<<": ";
		solve();
	}
	#ifdef LOCAL
		cerr<<endl<<"[Time Elapsed : "<<elapsed_time<<"]"<<endl;
	#endif
	return 0;
}

/*
   check for overflows int long long
   correct mize of array
*/
#include<bits/stdc++.h>
#define ll long long
using namespace std;
int main()
{
    double v,t,s,d;
    cin>>v>>t>>s>>d;
    double x = d/v;
    if(x<t||x>s)puts("Yes");
    else puts("No");
    return 0;
}
