Number of n-queens placements HARD Backtracking (BAC) 50 XP 0 solved
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Problem

On an `n x n` chessboard, place `n` queens so that no two attack each other (no two queens share a row, column, or diagonal). Read the positive natural number `n`. Determine and print the total number of valid arrangements.

Input format

Input input.txt

The program reads from standard input a single natural number, `n`. - `1 <= n <= 8` - For `n = 2` and `n = 3` the answer is `0`.

Output format

Output output.txt

The program prints a single natural number followed by a newline: the number of valid arrangements.

Example

input
4
output
2

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