8364번 - Idempotent Functions 다국어

문제

You are given a positive integer n. By A we mean the set {1, 2, 3, ..., n}. Function f : A → A is called a permutation if it is injective (for distinct arguments returns distinct values). Function f : A → A is called idempotent if for every i ∈ A holds f(f(i)) = f(i).

You are given a function f : A → A. How many pairs of functions (g, h) satisfy following conditions:

• g : A → A is a permutation,
• h : A → A is idempotent,
• for every i ∈ A holds f(i) = h(g(i))?

Write a program which:

• reads number n and description of function f from the standard input ,
• determines the number of pairs of functions (g, h) satisfying the requirement described above,
• writes the result to the standard output.

입력

In the first line of input there is one integer n (1 ≤ n ≤ 200 000). Second line contains a description of function f : f(i) (1 ≤ f(i) ≤ n) for i = 1, ..., n, separated with single spaces.

출력

In the first line of output there should be a single integer: the remainder of the division by 1 000 000 007 of the number of different pairs of functions (g, h) satisfying the requirement.

제한

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