def out(s, depth)
  (1..depth).each do |_|  print ' ' end
  puts s
end

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

  hn_bk = Array.new(hn)

  min = hn.min
  if n == 1
    #out("solve(#{n} #{hn}) = #{min}", depth)
    return min
  end

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

  start = hn[0] == 0 ? 1 : 0
  i = start
  ans = 0
  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

  #out("solve(#{n}, #{hn_bk}) = solve(#{n}, #{hn}) + min = #{ans} + #{min}", depth)

  min + ans
end

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

puts solve(n, hn, 0)
