#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(n) begin(n), end(n)
using ll = long long;
using namespace std;

int main(){
  ll l, r, m, k;
  cin >> l >> r >> m >> k;
  ll w = r - l;
  ll llim = l * k;
  ll mllim = llim % m;
  ll mr = w*k + mllim;
  if(m <= mr || mllim == 0){
    cout << "Yes" << endl;
  }else{
    cout << "No" << endl;
  }
  return 0;
}