N = gets.to_i
B = gets.split.map(&:to_i)
S = Array.new(N + 1, 0)
B.each_with_index do |b,i|
  S[i + 1] = S[i] + b
end
t_ = (1 .. N).inject(0) do |t,n|
  if S[n] >= n
    t + S[n] - n
  else
    r = S.bsearch_index{|s| s >= n }
    t + r - n
  end
end
puts t_