Preparing NOJ

As you could know there are no male planes nor female planes. However, each plane on Earth likes some other plane. There are *n* planes on Earth, numbered from 1 to *n*, and the plane with number *i* likes the plane with number *f*_{i}, where 1 ≤ *f*_{i} ≤ *n* and *f*_{i} ≠ *i*.

We call a love triangle a situation in which plane *A* likes plane *B*, plane *B* likes plane *C* and plane *C* likes plane *A*. Find out if there is any love triangle on Earth.

The first line contains a single integer *n* (2 ≤ *n* ≤ 5000) — the number of planes.

The second line contains *n* integers *f*_{1}, *f*_{2}, ..., *f*_{n} (1 ≤ *f*_{i} ≤ *n*, *f*_{i} ≠ *i*), meaning that the *i*-th plane likes the *f*_{i}-th.

Output «YES» if there is a love triangle consisting of planes on Earth. Otherwise, output «NO».

You can output any letter in lower case or in upper case.

5

2 4 5 1 3

YES

5

5 5 5 5 1

NO

In first example plane 2 likes plane 4, plane 4 likes plane 1, plane 1 likes plane 2 and that is a love triangle.

In second example there are no love triangles.

Info

Provider CodeForces

Origin Codeforces Round #464 (Div. 2)

Code CF939A

Tags

Submitted 105

Passed 68

AC Rate 64.76%

Date 03/04/2019 16:19:43

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