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

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

ll l, r, m, k;


void solve() {
  cin >> l >> r >> m >> k;
  if (k == 0 || l == 0) {
    cout << "Yes" << endl;
    return;
  }
  string ans = "No";
  
  if ((r-l)*k >= m) {
    ans = "Yes";
  } else {
    if ((r*k)%m < (l*k)%m) ans = "Yes";
  }
  cout << ans << endl;
}


int main() {
  solve();
}