Tính tổng

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Problem type
Points: 100 (p) Time limit: 1.0s Memory limit: 256M Input: stdin Output: stdout

Tính \(F(n) = 1 * 2 + 2 * 3 + ... + (n-1) * n\)

Input

  • 1 dòng ghi số \(n\)

Output

  • In ra đáp án

Example

Test 1
Input 
2
Output 
2
Test 2
Input 
3
Output 
8

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