N = gets.to_i
A = gets.split.map(&:to_i)
S = gets.chomp

sum = 0
base = 1
S.each_char do |s|
  if s == '<'
    sum += base
  end

  base *= 2
end

v = 0
base = 1
A.each_cons(2) do |a, b|
  if a < b
    v += base
  end

  base *= 2
end

base = 2 ** (N - 2)

N.times do |i|
  if sum == v
    puts i
    exit
  end

  v /= 2
  A.rotate!(1)

  if A[-2] < A[-1]
    v += base
  end
end

puts -1