#include <iostream>
#include <queue>
#include <algorithm>
#include <set>
#include <vector>
#include <string>

using namespace std; using ll=long long; const int INF=1e9; using P=pair<ll,ll>;

int main() {
  int a,b,c,d; cin>>a>>b>>c>>d;
  int i=0;
  while(a>0&&c>0) {
    if (i%2==0) {
      c-=b;
    } else {
      a-=d;
    }
    i++;
  }
  //cout<<a<<" "<<c<<endl;
  if (a<=0) cout<<"No"<<endl;
  else cout<<"Yes"<<endl;
}