C++ :

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int a[1005];

int main() {
  //freopen("Dongqi.in", "r", stdin);
	//freopen("Dongqi.out", "w", stdout);
  int n;
  a[1] = 4;
  for (int i = 2; i <= 1000; i++) {
    a[i] = a[i - 1] + 8;
  }
  while (scanf("%d", &n) != EOF) {
    if (n == 0)
      break;
    else
      printf("%d\n", a[n]);
  }
  return 0;
}