Avoid the Set {010, 101}

Difficulty: 2400 4000 ms 128 MB

combinatorics aho-corasick matrix-exponentiation

Count the strings of length N over {0, 1} that contain none of 010, 101 as a substring, modulo 10⁹+7.

Input: one integer N.

Output: the count mod 10⁹+7.

Constraints:

• 1 ≤ N ≤ 10¹⁸

Sample Tests

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2

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4

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