lib C
  fun strtoll(s : UInt8*, p : UInt8**, b : Int32) : Int64
end

class String
  def to_i64
    C.strtoll(self, nil, 10)
  end
end

n, k = read_line.split.map(&.to_i64)
a = read_line.chars.map(&.to_i)

MAX_B = 32
dp = Array.new(MAX_B) { Array.new(n, 0i64) }

(0...n).each do |start|
  now = 1
  (1..n).each do |cnt|
    i = (start + cnt - 1) % n
    now = now + a[i] - 1
    if now == 0
      dp[0][start] = cnt.to_i64
      break
    elsif cnt == n
      dp[0][start] = k + 1
    end
  end
end

(0...MAX_B - 1).each do |k|
  (0...n).each do |i|
    next_i = (dp[k][i] + i) % n
    dp[k + 1][i] = dp[k][i] + dp[k][next_i]
  end
end

puts (1i64..k).bsearch { |buy|
  ice, now = 0i64, 0
  (0...MAX_B).each { |bit|
    if buy.bit(bit) == 1
      ice += dp[bit][now]
      now = (dp[bit][now] + now) % n
    end
  }
  ice >= k
}