#include <bits/stdc++.h>

using namespace std;
using ll = long long;

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