C :

#include<stdio.h>
int main(){
	int sum=0;
	int n,i;
	scanf("%d",&n);
	for(i=1;i<=n;++i){
		sum+=3*i-1;
	}
	printf("%d",sum);
	return 0;
}

C++ :

#include<iostream>
using namespace std;

int main() {
	int n;
	cin >> n;
	int sum = 0;
	int j = 2;
	for(int i=0; i<n; ++i){
		sum += j;
		j += 3;
	}
	cout << sum << endl;
	return 0;
}