#include <iostream>

using namespace std;

const long MOD = 1000000007;
typedef pair<int, int> P;
typedef long long ll;

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

    int t, a;

    if(C % B == 0) t = C / B;
    else t = C/B + 1;

    if(A%D == 0) a = A/D;
    else a = A/D+1;

    if(t <= a) cout << "Yes" << endl;
    else cout << "No" << endl;

    return 0;
}
