#include <bits/stdc++.h>
#define rep(i,n) for (int i=0;i<(n);i++)
#define adrep(i,s,n) for (int i=(s);i<(n);i++)
using namespace std;
typedef long long ll;

int main(){

  int a,b,c,d=0;
  cin>>a>>b>>c>>d;
	

  while(1){

    c-=b;
    if(c<=0){cout<<"Yes"<<endl;return 0;}
    a-=d;
    if(a<=0){cout<<"No"<<endl; return 0;}
    
  }

}