#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=floor(bian)*floor(bian)+4*floor(bian);
        bian+=0.000001;
    }
    double r;
    r=sqrt((bian/2.0)*(bian/2.0)+((bian+2.0)/2.0)*((bian+2.0)/2.0));
    cout<<fixed<<setprecision(10)<<r;
    return 0;
}