#include <bits/stdc++.h>
#define MODNum 1000000007
#define REP(type, i, a, b) for( type i = a; i < b; i++ )
typedef long long ll;

using namespace std;

int main (void) {
    ll L, R, M, K;
    cin >> L >> R >> M >> K;
    ll Left  = K * L;
    ll Right = K * R;
    if ( K == 0 || L == 0 ){
        cout << "Yes" << endl;
        return 0;
    }
    if ( Right - Left >= M ){
        cout << "Yes" << endl;
        return 0;
    }
    if ( Right >= M && Left <= M ){
        cout << "Yes" << endl;
        return 0;
    }
    else{
        if ( Right < M ){
            cout << "No" << endl;
            return 0;
        }
        else{
            Left %= M; Right %= M;
            if ( Right >= M && Left <= M ){
                cout << "Yes" << endl;
                return 0;
            }
            else{
                cout << "No" << endl;
                return 0;
            }
        }
    }
    return 0;
}