require 'matrix'

N, K = gets.split.map(&:to_i)
S = gets.chomp
def f(s, i, m)
  if i == s.size
    Vector[0, m]
  elsif m > 0
    f(s, i + 1, m - 1 + s[i].to_i)
  else
    f(s, i + 1, s[i].to_i) + Vector[1, 0]
  end
end
a, b = f(S, 0, 0).to_a
ans = if K < N
        f(S[0...(K % N)], 0, 0)[0]
      else
        a + (K / N - 1) * [a - b, 0].max + f(S[0...(K % N)], 0, b)[0]
      end
puts ans