#include<bits/stdc++.h>
using namespace std;

#define int long long

int s;

double mysqr(double x)
{
    if(x<0)
        return 0;
    return sqrt(x);
}

int chk(double R)
{
    int ret=0;
    for(int i=1;i<=R;i++)
        ret+=(int)mysqr(R*R-i*i);
    return ret;
}

signed main()
{
    scanf("%lld",&s);
    double l=0,r=2e5;
    // cout<<chk(2.2360679775)<<endl;
    for(int T=1;T<=100;T++)
    {
        double mid=(l+r)/2;
        if(chk(mid)*4>=s)
            r=mid;
        else
            l=mid;
    }
    printf("%.10lf\n",r);
}