A. 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
4
output
2
input
5
output
-3
Note
f(4) = - 1 + 2 - 3 + 4 = 2
f(5) = - 1 + 2 - 3 + 4 - 5 = - 3
# include<cstdio>
# include<iostream>
using namespace std;
int main(void)
{
long long n;
while(scanf("%lld",&n)!=EOF)
{
if ( n%2 == 0 )
printf("%lld\n",n/2);
else
printf("%lld\n",n/2-n);
}
return 0;
}