N, K = gets.split.map(&:to_i)
A = gets.split.map(&:to_i)

ac = 0
wa = 10**20
while wa - ac > 1
    wj = (ac + wa) >> 1
    
    add = 0
    count = 0
    N.times do |i|
        if A[i] + add < wj
            c = (wj - (A[i] + add) + i) / (i + 1)
            count += c
            add += c * (i + 1)
        end
    end
    
    if count <= K
        ac = wj
    else
        wa = wj
    end
end

puts ac