def f(cnt, ind)
  x = ind.tally.min_of { |elem, c| cnt[elem] // c }
  ind.each { |i| cnt[i] -= x }
  x
end

n = read_line.to_i
s = read_line
cnt = [s.count('z'), s.count('y'), s.count("v-x"), s.count('u'), s.count("l-t"), s.count('k'), s.count('j'), s.count('i'), s.count("a-h")]

puts [
  [0],
  [1, 2],
  [1, 3, 4],
  [1, 3, 5, 6],
  [1, 3, 5, 7, 8],
  [1, 3, 5, 7, 7],
  [1, 3, 5, 5],
  [1, 3, 3],
  [1, 1],
].sum { |ind|
  f(cnt, ind)
}