#include <iostream>
#include <algorithm>
#define flush fflush(stdout)
using namespace std;
typedef long long ll;
typedef pair<ll, int> P;
const int mod = (int)1e9 + 7, INF = (int)1e9;
const int di[4] = { 1,0,-1,0 }, dj[4] = { 0,1,0,-1 };


int main(void) {
	int a, b, c, d;

	scanf("%d%d%d%d", &a, &b, &c, &d);

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

	return 0;
}