#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=200005;
const double hu=3.14159265358*10/4.0;
int n;
double ans;
void solve(){
	cin>>n;
	int k=0;
	double a,b;
	if(n==1){
			ans=1.4142135624;
	printf("%.10lf",ans);
	return;}
	int f=0;
	int minl=1e11;
	for(int i=sqrt(1e9) ;i>=0;i--){
		if(i*i-n>=0&&(i*i-n)<minl){
			minl=i*i-n;
			k=i;
		}
		else break;
	}
//	cout<<k<<endl;
	if(k*k==n){
		a=k+2,b=k;
	}
	else if(k*k-4>=n){
		a=k-2,b=k;
	}
	else {
		a=k,b=k;
	}	
//	cout<<a<<" "<<b<<endl;
	ans=sqrt(a*a+b*b)/2.0;
	printf("%.10lf",ans);
	return;
}
signed main() {
//	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	//freopen("in.txt","r",stdin);
	//freopen("out.txt","w",stdout);
	int T_case=1;
//	cin>>T_case;
	while(T_case--){
		solve();
	}
    return 0;
}