import java.io.*;
import java.util.*;

public class Semordnilaps {

    public static void main(String[] args) throws IOException {
        List<String> lst = readLines("unixdict.txt");
        Set<String> seen = new HashSet<>();
        int count = 0;
        for (String w : lst) {
            String r = new StringBuilder(w).reverse().toString();
            if (seen.contains(r)) {
                if (count++ < 5)
                    System.out.printf("%-10s %-10s\n", w, r);
            } else seen.add(w);
        }
        System.out.println("\nSemordnilap pairs found: " + count);
    }

    private static List<String> readLines(String fn) throws IOException {
        List<String> lines;
        try (BufferedReader br = new BufferedReader(new FileReader(fn))) {
            lines = new ArrayList<>();
            String line;
            while ((line = br.readLine()) != null)
                lines.add(line.trim().toLowerCase());
        }
        return lines;
    }
}