题解

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

int a[60];

int main() {
	
	int n;
	cin >> n;
	a[1] = 3;
	for(int i = 2; i <= n; i++) {
		a[i] = a[i-1] + 4 * i - 2;
	} 
	cout << a[n]; 
	
	return 0;
}