#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;

	for(int i=sqrt(1e9) ;i>=0;i--){
		if( pow(i,2) <=n ){
			k=i;
			break;
		}
	}
//	cout<<k<<endl;
	if(k*k==n){
		a=k,b=k;
	}
	else if((k+1)*(k+1)-4>=n){
		k++;a=k,b=k-2;
	}
	else {
		a=k+1,b=k+1;
	}
//	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;
}