Problem:
Score : 100 points

Problem Statement

It is known that the area of a regular dodecagon inscribed in a circle of radius a is 3a^2.

Given an integer r, find the area of a regular dodecagon inscribed in a circle of radius r.

Constraints

1 \leq r \leq 100

r is an integer.

Input

Input is given from Standard Input in the following format:

r

Output

Print an integer representing the area of the regular dodecagon.

Sample Input 1

4

Sample Output 1

48

The area of the regular dodecagon is 3 \times 4^2 = 48.

Sample Input 2

15

Sample Output 2

675

Sample Input 3

80

Sample Output 3

19200

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include<bits/stdc++.h>
using namespace std;

// for loop
#define rep(i,a,n) for(int i=(a);i<(n);++i)
#define repe(i,a,n) for(int i=(a);i<=(n);++i)
#define rrep(i,n,a) for(int i=(n);n>(a);--i)
#define rrepe(i,n,a) for(int i=(n);n>=(a);--i)

// abbreviati
#define PB(v) push_back(v)
#define MP make_pair
#define F first
#define S second
#define all(v) v.begin(),v.end()
#define ENDL << "\n"

using ll = long long;
using P = pair<int,int>;
using itn = int;

// constant
const int INF = 1<<30;
const ll INFLL = 1LL << 60;
const ll MOD = 1000000007;
const long double PI =(acos(-1));

/***Snippet***************************************************
ifelse, isprime, torad, todeg, lcm, bfs,chmin,chmax
**************************************************************/

// adjacency list
vector<int> to[100005];

// Graph
using Graph = vector<vector<int>>;

// Grid
int H,W;
vector<vector<int>> field;

// 4方向への移動ベクトル
const int dx[4]={1,0,-1,0};
const int dy[4]={0,1,0,-1};


int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int r;cin >> r;
    cout << 3*r*r ENDL;
    
    return 0;
}