One day, Twilight Sparkle is interested in how to sort a sequence of integers a₁, a₂, ..., a_n in non-decreasing order. Being a young unicorn, the only operation she can perform is a unit shift. That is, she can move the last element of the sequence to its beginning:

Help Twilight Sparkle to calculate: what is the minimum number of operations that she needs to sort the sequence?

The first line contains an integer n(2 ≤ n ≤ 10⁵). The second line contains n integer numbers a₁, a₂, ..., a_n(1 ≤ a_i ≤ 10⁵).

If it's impossible to sort the sequence output -1. Otherwise output the minimum number of operations Twilight Sparkle needs to sort it.