#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1000000007;
const long long INF = 9999999999999999;
using ll = long long;
int main(){
  int A,B,C,D;
  cin>>A>>B>>C>>D;
  int F,G;
  if(A%B != 0){
    F = A/B;
    F++;
  }
  else{
    F = A/B;
  }
  if(c%D != 0){
    G = C/D;
    G++;
  }
  else{
    G = C/D;
  }
  if(F>=G){
    cout << "Yes" << endl;
  }
  else{
    cout << "No" << endl;
  }
  return 0;
}