#include <iostream>
#include <algorithm>
#include <iomanip>
using namespace std;
using ll = long long;
#define pi 3.1415926
 
int a[3];
 
int main()
{
    int a, b, c, d;
    cin >> a >> b >> c >> d;
    while(a){
        c = c - b;
        if(c <= 0){  
            cout << "Yes";
            break;
        }
        a = a - d;
        if(a <= 0){
            cout << "No";
            break;
        }
    }
}
