Codeforces Round #277 (Div. 2)---A. Calculating Function （规律） - c++编程基础

Calculating Function
time limit per test 1 second memory limit per test 256 megabytes input standard input output standard 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 
  
   
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               using namespace std; #define INF 0x7fffffff int 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; }