#include<bits/stdc++.h>
//cervello|Phoenix
using namespace std;
#define ll long long int
#define eb emplace_back
#define mk make_pair
#define pr pair<int,int>
#define all(x) x.begin(),x.end()
#define mod 1000000007

int main(){
  ios_base::sync_with_stdio(false);
    // #ifndef ONLINE_JUDGE
    //   freopen("input.txt", "r", stdin);
    //   freopen("output.txt", "w", stdout);
    // #endif
  int a,b,c,d; cin>>a>>b>>c>>d;
  while(a>0&&c>0){
    c-=b;
    if(c<=0){
      cout<<"Yes\n";
      return 0;
    }
    a-=d;
    if(a<=0){
      cout<<"No\n";
      return 0;
    }
  }
  return 0;
}