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:
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,...,an (1≤ai≤105).
If it's impossible to sort the sequence output -1. Otherwise output the minimum number of operations Twilight Sparkle needs to sort it.
2
2 1
1
3
1 3 2
-1
2
1 2
0