#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main() {
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    int taka;
    if(c%b==0){
        taka=c/b;
    }else{
        taka=c/b+1;
    }
    int aoki;
    if(a%d==0){
        aoki=a/d;
    }else{
        aoki=a/d+1;
    }
    if(taka<=aoki){
        cout<<"Yes"<<endl;
    }else{
        cout<<"No"<<endl;
    }
}