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P165SUMI - ROUND 5I - Cộng trừ

Bạn hãy tính tổng S = -1 + 2 – 3 + … + ((-1) ^ n) * n.

Input

Một số nguyên n (1 <= n <= 10^15)

Output

In ra giá trị S.

Example

Test 1:
Input:
4
Output:
2
Test 2:
Input:
5
Output:
-3

Được gửi lên bởi:Admin
Ngày:2016-08-05
Thời gian chạy:1s
Giới hạn mã nguồn:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
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