#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <cmath>
#include <functional>
#include <set>
#include <ctime>

using namespace std;
typedef long long ll;

int __gcd(int x, int y)
{
    if (y == 0) return x;
    return __gcd(y, x % y);
}


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

    return 0;
}