#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int a, b, c;
  cin >> a;
  b = a % 10;
  c = a / 10;
  if (b == 9)
    cout << -(c * 5 + 5);
  else if (b == 8)
    cout << c * 5 + 4;
  else if (b == 7)
    cout << -(c * 5 + 4);
  else if (b == 6)
    cout << c * 5 + 3;
  else if (b == 5)
    cout << -(c * 5 + 3);
  else if (b == 4)
    cout << c * 5 + 2;
  else if (b == 3)
    cout << -(c * 5 + 2);
  else if (b == 2)
    cout << c * 5 + 1;
  else if (b == 1)
    cout << -(c * 5 + 1);
  else
    cout << c * 5;
  return 0;
}

### Prompt

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

For a positive integer n let's define a function f:

f(n) = - 1 + 2 - 3 + .. + ( - 1)nn

Your task is to calculate f(n) for a given integer n.

Input

The single line contains the positive integer n (1 ≤ n ≤ 1015).

Output

Print f(n) in a single line.

Examples

Input

4


Output

2


Input

5


Output

-3

Note

f(4) = - 1 + 2 - 3 + 4 = 2

f(5) = - 1 + 2 - 3 + 4 - 5 = - 3

### Response

```cpp
#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int a, b, c;
  cin >> a;
  b = a % 10;
  c = a / 10;
  if (b == 9)
    cout << -(c * 5 + 5);
  else if (b == 8)
    cout << c * 5 + 4;
  else if (b == 7)
    cout << -(c * 5 + 4);
  else if (b == 6)
    cout << c * 5 + 3;
  else if (b == 5)
    cout << -(c * 5 + 3);
  else if (b == 4)
    cout << c * 5 + 2;
  else if (b == 3)
    cout << -(c * 5 + 2);
  else if (b == 2)
    cout << c * 5 + 1;
  else if (b == 1)
    cout << -(c * 5 + 1);
  else
    cout << c * 5;
  return 0;
}

```