#define _CRT_SECURE_NO_WARNINGS
#include<bits/stdc++.h>
#define f for
#define ll long long
#define ull unsigned long long
#define endl "\n"
using namespace std;
double pi = acos(-1);
void Open()
{
#ifndef ONLINE_JUDGE
freopen("Input.txt", "r", stdin);
freopen("Output.txt", "w", stdout);
#endif
}
//#define all(a) a.begin(), a.end()
ll gcd(ll a, ll b)
{
return b == 0 ? a : gcd(b, a % b);
}
void PrintNumber(int n, int len)
{
if (!len)
return;
cout << (n & 1);
}
void PrintAllSubset(int n)
{
f(int i = 0; i < (1 << n); i++)
{
PrintNumber(i, n);
cout << endl;
}
}
//int a[1000003];
int main()
{
//Open();
//freopen("mex.in","r",stdin);
std::ios_base::sync_with_stdio(0);
cin.tie(NULL);
//cout<<3;
map<int,bool>mp;
double r,a1,a2,a3;
cin>>r;
a1=r*(sqrt(r*r*3));
a2=3.141592*r*r;
a3=0.5*r*(sqrt(-(0.5*r)*(0.5*r)+r*r));
cout<<a1+a2-a3;
}
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