Codeforces Round #277 (Div. 2)-A. Calculating Function （规律）_html/css_WEB-ITnose

Calculating Function

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

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.

Sample test(s)

input

output

input

output

-3

Note

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

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

解题思路：大水题一枚，直接找规律。n%2==0时，f = n/2; 否则，f = -(n+1)/2.

AC代码：

#include #include #include #include #include #include #include #include