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
4
output
2
input
5
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 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;
}