#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  ll L, R, M, K;
  cin >> L >> R >> M >> K;

  ll KL = K*L;
  ll KR = K*R;

  ll target = KL + (M - (KL%M));
  if(KL%M==0) target = KL;

  if(target <= KR) cout << "Yes" << endl;
  else cout << "No" << endl;
  
  return 0;
}