n = read_line.to_i
s = read_line
sc = s.chars
set = Set(Array(Char)).new
i = 0
(n-1).times do |i|
    c1 = sc[i]
    c2 = sc[i+1]
    sc[i] = 'B'
    sc[i+1] = 'B'
    set << sc
    sc[i] = c1
    sc[i+1] = c2
    i += 1
end
puts set.size