#include <bits/stdc++.h>
#define l_ength size
const int inf = (1<<30);
const int mod = 1000000007; // 998244353
using ll = long long;
using namespace std;

int main(){
	int a, b, c, d; cin >> a >> b >> c >> d;
	while( true ){
		c -= b;
		if( c <= 0 ){
			cout << "Yes" << endl;
			return 0;
		}
		a -= d;
		if( a <= 0 ){
			cout << "No" << endl;
			return 0;
		}
	}
}