cf486A Calculating Function-白红宇

cf486A Calculating Function

阅读量：4677 次

发布时间：2019-06-09

本文共 1176 字，大约阅读时间需要 3 分钟。

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

一分钟就秒了

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                 #define LL long long#define inf 0x7ffffff#define pa pair
                 
                  #define pi 3.1415926535897932384626433832795028841971using namespace std;inline LL read(){ LL x=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} return x*f;}int main(){ LL n=read(); if (!(n&1))printf("%lld\n",n/2); else printf("%lld\n",n/2-n);}