#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
void solveCP311() {
  ll n;
  cin >> n;
  ll dp[n + 1];
  dp[0] = 0;
  dp[1] = 2;
  for (ll i = 2; i <= n; i++) {
    dp[i] = dp[i - 1] + (dp[i - 1] - dp[i - 2]) * 2;
  }
  cout << dp[n];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ll t = 1;
  while (t--) {
    solveCP311();
  }
  return 0;
}

### Prompt

Your challenge is to write a Cpp solution to the following problem:

The numbers of all offices in the new building of the Tax Office of IT City will have lucky numbers.

Lucky number is a number that consists of digits 7 and 8 only. Find the maximum number of offices in the new building of the Tax Office given that a door-plate can hold a number not longer than n digits.

Input

The only line of input contains one integer n (1 ≤ n ≤ 55) — the maximum length of a number that a door-plate can hold.

Output

Output one integer — the maximum number of offices, than can have unique lucky numbers not longer than n digits.

Examples

Input

2


Output

6

### Response

```cpp
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
void solveCP311() {
  ll n;
  cin >> n;
  ll dp[n + 1];
  dp[0] = 0;
  dp[1] = 2;
  for (ll i = 2; i <= n; i++) {
    dp[i] = dp[i - 1] + (dp[i - 1] - dp[i - 2]) * 2;
  }
  cout << dp[n];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ll t = 1;
  while (t--) {
    solveCP311();
  }
  return 0;
}

```