#include <iostream>
#include <vector>
#include <algorithm>

using namespace std; using ll=long long; const ll LNF=1e18; const int INF = 1e9+1; const ll M = 1e9+7;
typedef pair<int,int> P;

int main() {
  ll l,r,m,k; cin>>l>>r>>m>>k;
  ll p = (m*m-l*k)%m;
  if ((r-l)*k>=p) cout<<"Yes"<<endl;
  else cout<<"No"<<endl;
}