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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

//JSD
#include<iostream>
#include<vector>
#include<map>
#define ll long long
using namespace std;
int main(){
	int n;
	cin>>n;
	ll sum=0;
	int a[n+1],b[n+1];
	for(int i=1;i<=n;i++) cin>>a[i],b[i]=a[i];
	for(int i=n/2;i>=1;i--){
		ll ans=0;
		for(int j=2;j*i<=n;j++){
			ans+=b[j*i];
		}
		ans=ans%2;
		if(a[i]==1){
			if(ans==1) b[i]=0;
			else b[i]=1;
		}
		else{
			if(ans==1) b[i]=1;
			else b[i]=0;
		}
	}
	vector<int > v;
	for(int i=1;i<=n;i++){
		if(b[i]==1)
		v.push_back(i);
	}
	cout<<v.size()<<"\n";
	for(int i=0;i<v.size();i++) cout<<v[i]<<" ";
	return 0;
}