def solve(n, hn, depth)
  return 0 if n == 0

  min = hn.min
  return min if n == 1

  (0..n-1).each { |i| hn[i] -= min}

  start = hn[0] == 0 ? 1 : 0
  i = start
  ans = min
  while i < n do
    if hn[i] == 0
      tmp = solve(i - start, hn[start..(i-1)], depth + 1)
      ans += tmp
      start = i + 1
    end

    i += 1
  end
  if hn[i-1] != 0
    ans += solve(i - start, hn[start..(i-1)], depth + 1)
  end

  ans
end

n = gets.to_i
hn = gets.split.map(&:to_i)

puts solve(n, hn, 0)
