#include<bits/stdc++.h>
#include <string>

using namespace std;
double bin_search(double n,double l,double r){
    double mid=(l+r)/2;
    double ans=(mid*mid)+sqrt(mid);
    if((r-l)<(0.0000001)){
        return r;
    }
    if(ans>=n){
        return bin_search(n,l,mid);
    }
    else{
        return bin_search(n,mid+0.0000001,r);
    }
}

int main()
{
    double n,b;
    cin>>n;
    double ans=bin_search(n,0,10000);
    cout<<ans;
       return 0;
}