#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const  ll INF = 1e9;
const  ll MOD = 1e9 + 7;
#define all(v) v.begin(), v.end()
#define repi(i,n,init) for(ll i=init;i<(n);i++)
#define repd(i,n,init) for(ll i=(n);i>=init;i--)
#define repm(i,m) for(auto i=m.begin();i!=m.end();i++)
#define repb(bit,n,init) for(ll bit=init;bit<(1<<n);++bit)

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