// Author :- Sarvesh Chaudhary
#include<bits/stdc++.h>
using namespace std;
#define w(x) int x; cin>>x; while(x--)
#define ll long long int
#define sidha(i,a,b) for(int i=a;i<b;i++)
#define set_built(x) __builtin_popcountll(x)
#define zero_built(x) __bultin_ctzll(x)
#define pairi pair<int,int>
#define vi vector<int>
#define mod 1000000007
#define MAX INT_MAX
#define MIN INT_MIN
#define pb push_back
#define po pop_back
#define all(c) c.begin(),c.end()
#define io ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

//Global Variable
map<int,int> m;

//Functions


//Driver Function
int main(){
	io;
    double a,b,c,d;cin>>a>>b>>c>>d;
    double x=d/a;
    if(x>c or x<b){
        cout<<"Yes"<<endl;
    }
    else{
        cout<<"No"<<endl;
    }
	return 0;
}
#include<bits/stdc++.h>
#define lli long long int
using namespace std;

int main()
{
    lli a,b,c,d,t,n,x,y,z,i,j,k,s,v;
    cin>>v>>s>>t>>d;
    if(d>=v*s && d<=v*t)
    {
        cout<<"No"<<endl;
    }
    else
    {
        cout<<"Yes"<<endl;
    }
    return 0;
}
