/**
* @brief Codeforces Round #277 (Div. 2) a
* @author xiyan
* @created 2014/11/13 11:23
* @edited 2014/11/13 11:24
* @type math
*
*
*/
#include <stdio.h>
long long int a;
int main()
{
scanf("%I64d", &a);
printf("%I64d\n", (a >> 1) - ( a &0x1 ? a : 0));
return 0;
}
Codeforces Round #277 (Div. 2) a
原文：http://my.oschina.net/u/572632/blog/343892