#include<bits/stdc++.h>
#define INF 400010
#define mod 80112002
using namespace std;
typedef long long LL;
int a[INF];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin>>n;
    double minn=1,bian=1;
    while(minn<=n)
    {
        minn=bian*bian+4*bian;
        bian++;
    }
    double temp=bian-1;
    minn=1;
    if(n==1)
    {
        cout<<1.4142136;
        return 0;
    }
    while(temp<=bian&&minn<=n)
    {
        minn=floor(temp)*floor(temp)+4*floor(temp);
        temp+=0.000000001;
    }
    double r;
    r=sqrt((temp/2.0)*(temp/2.0)+((temp+2.0)/2.0)*((temp+2.0)/2.0));
    cout<<fixed<<setprecision(10)<<r;
    return 0;
}