#include <bits/stdc++.h>
int main() {
  long long x;
  scanf("%I64u", &x);
  if (x % 2 == 0) {
    printf("%I64d", x / 2);
  } else {
    printf("%I64d", -(x / 2 + 1));
  }
  exit(EXIT_SUCCESS);
}

### Prompt

Please provide a CPP coded solution to the problem described below:

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>
int main() {
  long long x;
  scanf("%I64u", &x);
  if (x % 2 == 0) {
    printf("%I64d", x / 2);
  } else {
    printf("%I64d", -(x / 2 + 1));
  }
  exit(EXIT_SUCCESS);
}

```