A. Calculating Function
Time Limit: 20 Sec
Memory Limit: 256 MB
题目连接
http://codeforces.com/contest/486/problem/A
Description
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 Input
4
Sample Output
2
HINT
题意
f(n) = - 1 + 2 - 3 + .. + ( - 1)^n
给你n，然后让你求f(n)
题解：
分奇偶啦，奇数就是(n-1)/2-n，偶数就是n/2
代码
#include<stdio.h>
#include<iostream>
using namespace std;
int main()
{
long long n;scanf("%lld",&n);
if(n%==) printf("%lld\n",(n-1LL)/2LL - n);
else printf("%lld\n",n/2LL);
}