N = gets.to_i
S = gets.chomp.chars.sort.reverse
T = 'yuki'

def f(x)
  completed = Array.new(x, false)
  idx = 0

  5.times do |i|
    x.times do |j|
      next if completed[j]
      return false if N <= idx

      if T[i] < S[idx] || i == 4
        completed[j] = true
      elsif T[i] == S[idx]
        # NOOP
      else
        return false
      end

      idx += 1
    end
  end

  true
end

ok = 0
ng = N + 1

while (ok - ng).abs >= 2
  x = (ok + ng) / 2

  if f(x)
    ok = x
  else
    ng = x
  end
end

puts ok