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

int main() {
  int A,B,C,D;
  cin >> A >> B >> C >> D;
  int x=(A-1)/D;
  int y=(C-1)/B;
  if(x>=y){
    cout << "Yes" <<  endl;
  }
  else{
    cout << "No" << endl;
  }
}
