#include <bits/stdc++.h>
#define ALL(v) v.begin(), v.end()
#define ALLG(v) v.begin(), v.end() ,greater<int>()
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
ll GCD(ll x, ll y) { return y ? GCD(y, x % y) : x; }
ll LCM(ll x, ll y) { return x * y / GCD(x, y); }
ll GetDigit(ll num) {
	ll digit = 0;
	while (num != 0) {
		num /= 10;
		digit++;
	}
	return digit;
}

using namespace std;
int main() {
	int a, b ,c,d;
	cin >> a >> b >> c >> d;


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




}