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

int main() {
    int a = 0;
    int b = 0;
    int c = 0;
    int d = 0;
    cin >> a >> b >> c >> d;
    
    while(1){
        c -= b;
        if(c <= 0){
            cout << "Yes" << endl;
            break;
        }
        a -= d;
        if(a <= 0){
            cout << "No" << endl;
            break;
        }
    }
    
    return 0;
}