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

Calculating Function

time limit per test

memory limit per test

input

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 <stdio.h>#include <string.h>#include <iostream>#include <algorithm>#include <vector>#include <queue>#include <set>#include <map>#include <string>#include <math.h>#include <stdlib.h>#include <time.h>using namespace std;#define INF 0x7fffffffint main(){//    #ifdef sxk//        freopen("in.txt","r",stdin);//    #endif    long long n;    while(scanf("%lld",&n)!=EOF)    {        if(n & 1) printf("%lld\n", -(n+1)/2);        else printf("%lld\n", n/2);    }    return 0;}</time.h></stdlib.h></math.h></string></map></set></queue></vector></algorithm></iostream></string.h></stdio.h>