package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
)

func uniq(input io.Reader, output io.Writer) error {
	in := bufio.NewScanner(input)
	var prev string
	for in.Scan() {
		txt := in.Text()

		if txt == prev {
			continue
		}

		if txt < prev {
			return fmt.Errorf("file not sorted")
		}

		prev = txt
		fmt.Fprintln(output, txt)
	}
	return nil
}

func main() {
	err := uniq(os.Stdin, os.Stdout)
	if err != nil {
		panic(err.Error())
	}

	/*
		// Вариант с map плох для больших объемов данных
		in := bufio.NewScanner(os.Stdin)
		alreadySeen := make(map[string]bool)
		for in.Scan() {
			txt := in.Text()

			if _, found := alreadySeen[txt]; found {
				continue
			}

			alreadySeen[txt] = true

			fmt.Println(txt)
		}
	*/
}