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
问题链接:http://codeforces.com/problemset/problem/486/A
问题简述:输入一个数,算出-1+2+…+(-1)^n*n
问题分析:模拟过程
AC通过的C++语言程序如下:
#include <iostream>
using namespace std;
int main()
{
long long n;
cin >> n;
if (n % 2 != 0)
{
cout << ((n + 1) / 2)*(-1);
}
else
{
cout << n / 2;
}
return 0;
}