#include<iostream>
#include<stdio.h>
#include<string>
#include<vector>
#include<map>
#include<tuple>
#include<algorithm>
#include<cmath>
#include<limits>
#include<set>
#include<deque>
#include<queue>
using namespace std;
#define int long  long int
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
int lcm(int a, int b) { return a / gcd(a, b) * b; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
typedef pair<int, int>P;
const int MOD = 1e9 + 7;
//const int MOD = 998244353;
const int INF = 1e11;
const long double PI = (acos(-1));


signed main() {
	int A, B, C, D;
	cin >> A >> B >> C >> D;
	int turn = 0;
	while (1) {
		if (A <= 0) {
			cout << "No";
			return 0;
		}
		if (C <= 0) {
			cout << "Yes";
			return 0;
		}
		if (turn == 0) {
			C -= B;
			turn = 1;
		}
		else {
			A -= D;
			turn = 0;
		}
	}
}