Codeforces 630D. Hexagons! Solution

Solve in  C++:
///**********ALLAH IS ALMIGHTY************///
///AH Tonmoy
///Department of CSE
///Islamic University,Bangladesh
#include<iostream>
using namespace std;
int main()
{
    long long int n,a,r;
    cin>>a;
    n=a+1;
    r=3*n*(n-1)+1;

    cout<<r<<endl;

}