#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<set>
#include<queue>
#define _USE_MATH_DEFINES
#include<math.h>
#include<cmath>
#include<ctime>
#include<map>
#define R(i, n) for(int i = 0;i < n;i++)
#define S(a) scanf("%d", &a)
#define S2(a, b) scanf("%d%d", &a, &b)
#define S3(a, b, c) scanf("%d%d%d", &a, &b, &c)
#define SL(a) scanf("%lld", &a)
#define SL2(a, b) scanf("%lld%lld", &a, &b)
#define SL3(a, b, c) scanf("%lld%lld%lld", &a, &b, &c)
#define SA(i, n, a) R(i, n) scanf("%d", a + i)
#define SAL(i, n, a) R(i, n) scanf("%lld", a + i)
#define P(a) printf("%d", a)
#define PL(a) printf("%lld", a)
using namespace std;
using ll = long long;
using PR = pair<int, int>;
const ll MOD = 1e+9 + 7;
const int INF = 1e+9;

int A, B, C, D;

int main() {
	S3(A, B, C);
	S(D);
	bool flag = true;
	while (true) {
		C -= B;
		if (C <= 0)break;
		A -= D;
		if (A <= 0) {
			flag = false;
			break;
		}
	}
	if (flag)printf("Yes");
	else printf("No");
}
	