#include <fstream>
#include <iostream>
#include <set>
#include <string>

int main() {
    std::ifstream input("unixdict.txt");
    if (input) {
        std::set<std::string> words; // previous words
        std::string word; // current word
        size_t count = 0; // pair count

        while (input >> word) {
            std::string drow(word.rbegin(), word.rend()); // reverse
            if (words.find(drow) == words.end()) {
                // pair not found
                words.insert(word);
            } else {
                // pair found
                if (count++ < 5)
                    std::cout << word << ' ' << drow << '\n';
            }
        }
        std::cout << "\nSemordnilap pairs: " << count << '\n';
        return 0;
    } else
        return 1; // couldn't open input file
}