N = gets.to_i
S = gets.chomp
L = S.size

counter = Array.new(3) { Hash.new(0) }

L.times do |i|
  s = S[i]

  counter[i % 3][s] += 1
end

ans = 0
ans += [counter[0]['c'], counter[1]['o'], counter[2]['n']].min
ans += [counter[1]['c'], counter[2]['o'], counter[0]['n']].min
ans += [counter[2]['c'], counter[0]['o'], counter[1]['n']].min

puts ans