#include <bits/stdc++.h>
typedef long long int ll;
#define rep(i,n) for (int i = 0; i< (n); i++)
#define Rep(i,n,m) for (int i = (n); i< (m); i++)
#define Sort(a) sort(a.begin(), a.end())
#define Reverse(a) reverse(a.begin(), a.end())
const int INF = 1e9;
const ll MOD = 1000000007;
const ll LINF = 1e18;
using namespace std;



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

