#include <bits/stdc++.h>
 
using namespace std;
 
#define FOR(i, n) for(int i = 0; i < (int) n; i++)
#define rall(x) x.rbegin(), x.rend()
#define all(x) x.begin(), x.end()
#define PB push_back
#define F first
#define S second
 
typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
 
const ll MOD = 1e9+7;

int main(){
	ios::sync_with_stdio(false); cin.tie(0);
 	
 	int a, b,c, d; cin >> a >> b >> c >> d; 

 	while(1){
 		c -= b;
 		if(c <= 0){
 			cout << "Yes\n";
 			return 0;
 		}
 		a -= d;
 		if(a <= 0){
 			cout << "No\n";
 			return 0;
 		}
 	}



	return 0;
}