#!/usr/bin/ruby

def checkSquareBrackets(line)
	count = 0
	line.each_char do |char|
		if char == '['
			count += 1
		elsif char == ']'
			count -= 1
		end
		if count < 0
			return false
		end
	end
	if count!=0
		return false
	end
	return true
end

def checkChar(char)
	return char == '+' || char == '-' || char == '[' || char == ']' || (('a'..'z').include? char) || (('0'..'9').include? char) || (('BDIPSX').include? char)
end

def ok()
	puts "OK"
end

def error()
	puts "ERROR"
end

def checkLine(line)
	if checkSquareBrackets(line)
		base_found = false
		index_found = false
		var_found = false
		pos_var = false
		expression_start = true
		mem_chr = nil
		mem_no = nil
		sign_present = false
		line.each_char do |char|
			if checkChar(char)
				if expression_start && (char == '+' || char == '-')
					error()
					return
				end
				if char == ']' && sign_present
					error()
					return
				end
				if ('a'..'z').include? char.downcase
					if mem_chr
						reg = mem_chr.downcase + char.downcase
						if reg == 'bp' || reg == 'bx'
							if base_found
								error()
								return
							else
								base_found = true
							end
						elsif reg == 'si' || reg == 'di'
							if index_found
								error()
								return
							else
								inedx_found = true
							end
						else
							error()
							return
						end
						pos_var = false
					else
						if mem_no 
							error()
							return
						end
						pos_var = true
					end
				else
					if pos_var
						pos_var = false
						unless ('a'..'z').include? mem_chr
							error()
							return
						end
						if var_found
							error()
							return
						else
							var_found = true
						end
					end
				end
				if (('0'..'9').include? char) && mem_chr
					error()
					return
				end
				mem_chr = (('a'..'z').include? char.downcase) ? char : nil
				mem_no = (('0'..'9').include? char) ? char : nil
				expression_start = char == '['
				sign_present = char == '+' || char == '-'
			else
				error()
				return
			end
		end
		if pos_var && var_found
			error()
			return 
		end
		if sign_present
			error()
			return 
		end
		ok()
	else
		error()
	end
end

$stdin.each do |line|
	if line.length == 1 && line.chomp.length == 0
		break
	end
	line = line.chomp
	checkLine(line)
end