One day, Twilight Sparkle is interested in how to sort a sequence of integers a1, a2, …, an 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:
a1, a2, …, an → an, a1, a2, …, an - 1.
Help Twilight Sparkle to calculate: what is the minimum number of operations that she needs to sort the sequence?
Input
The first line contains an integer n(2 ≤ n ≤ 105). The second line contains n integer numbers a1, a2, …, an(1 ≤ ai ≤ 105).
Output
If it’s impossible to sort the sequence output -1. Otherwise output the minimum number of operations Twilight Sparkle needs to sort it.
