Description: 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 Format: The first line contains an integer n (2 ≤ n ≤ 105). The second line contains n integer numbers a1, a2, ..., an (1 ≤ ai ≤ 105). Output Format: If it's impossible to sort the sequence output -1. Otherwise output the minimum number of operations Twilight Sparkle needs to sort it. Note: None