#include <iostream>
#include <string>

using namespace std;

int main(){
    int A, B, C, D;
    cin >> A >> B >> C >> D;

    int atackA, atackB;
    atackA = C / B;
    if(C % B)
        atackA++;
    atackB = A / D;
    if(A % D)
        atackB++;
    string ans = "No";
    if(atackA <= atackB)
        ans = "Yes";
    cout << ans << endl;
    return 0;
}