#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <numeric>
using namespace std;

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

    while( true ){
        C = C - B;
        if( C<=0 ){
            break;
        }
        A = A - D;
        if( A<=0 ){
            break;
        }
    }

    if( A<= 0 ){
        cout << "No" << endl;
    }else if( C<=0 ){
        cout << "Yes" << endl;
    }

    return 0;
}