#include <bits/stdc++.h>
using namespace std;
long long int power(long long int a, long long int b);
int main() {
  long long int n, i, a = 2, sum = 0;
  cin >> n;
  for (i = 1; i <= n; i++) {
    sum += power(a, i);
  }
  cout << sum;
  return 0;
}
long long int power(long long int a, long long int b) {
  long long int value = 1, i;
  for (i = 1; i <= b; i++) {
    value = value * a;
  }
  return value;
}

### Prompt

Generate 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;
long long int power(long long int a, long long int b);
int main() {
  long long int n, i, a = 2, sum = 0;
  cin >> n;
  for (i = 1; i <= n; i++) {
    sum += power(a, i);
  }
  cout << sum;
  return 0;
}
long long int power(long long int a, long long int b) {
  long long int value = 1, i;
  for (i = 1; i <= b; i++) {
    value = value * a;
  }
  return value;
}

```