#include <iostream>
using namespace std;

//#include <ext/pb_ds/tree_policy.hpp>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
//template <typename T> using orderSet =
//tree <T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

typedef long long ll;
typedef unsigned long long llu;
#define filein freopen("input.txt", "r", stdin)
#define fileout freopen("output.txt", "w", stdout)
#define inf 1000000000000000018
#define mod 1000000007
#define ff first
#define ss second
#define pb push_back
#define mk make_pair
#define pii pair<int, int>
#define pll pair<ll, ll>

#define MX 200005

int main()
{
	ll a, b, c, d, x, y;
	cin>>a>>b>>c>>d;

	x = (c+b-1)/b;
	y = (a+d-1)/d;

    if(y < x) cout<<"No"<<endl;
    else cout<<"Yes"<<endl;
}
