Sum of the Sequence

Time Limit: 1 sec

 

The Problem

Given an interesting sequence in below. In this problem you have to find out the result of the sequence.

 

1 – 2 + 3 – 4 + 5 – 6 + 7 - . . . . . . . . . . . . . n =??

 

Example:

If n = 6 then

1 – 2 + 3 – 4 + 5 – 6 = -3

So the answer of this sequence is -3.

 

The Input

There are several lines of input. Each line contains a single integer n (1<= n <=5000000). Input is terminated by EOF.

 

The Output

For each line, output the line “Case T: R” (Quotes for clarification), where T denote the test case and R denotes the result of the sequence.

 

Sample Input

6

10

 

Sample Output

Case 1: -3

Case 2: -5

 

 

 

 

Problem Setter: Milton Deb