题解

#include<iostream>
using namespace std;
int main(){
	int n,a[105],i;
	cin>>n;
	a[1]=2; 
	for(int i=2;i<=n;i++){
		a[i]=a[i-1]+(4*i-3); 
	} 
	cout<<a[n]<<endl;
	return 0;
}