#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>
#include <unordered_map>

using namespace std;

unordered_map<string, vector<string>> c;

void generate(vector<string>& links, size_t pos, vector<string> built)
{
    static int64_t longest = 0;

    if (pos < links.size())
    {
        generate(links, pos + 1, built);
        built.push_back(links[pos]);
        generate(links, pos + 1, built);
        return;
    }

    if (built.size() <= 2)
        return;

    for (size_t i = 0; i < built.size(); i++)
        for (size_t j = 0; j < built.size(); j++)
        {
            if (i == j)
                continue;
            if (find(c[built[i]].begin(), c[built[i]].end(), built[j]) == c[built[i]].end())
                return;
        }

    if (built.size() > longest)
    {
        longest = built.size();
        sort(built.begin(), built.end());

        for (size_t i = 0; i < built.size(); i++)
            cout << built[i] << (i == built.size() - 1 ? "" : ",");
        cout << endl;
    }
}

int main()
{
    string line, c1, c2;
    ifstream inputfile("input.txt");

    while (getline(inputfile, line))
    {
        c1 = line.substr(0, 2), c2 = line.substr(3);
        if (find(c[c1].begin(), c[c1].end(), c2) == c[c1].end())
            c[c1].push_back(c2), c[c2].push_back(c1);
    }

    for (auto& it : c)
        generate(it.second, 0, vector<string>(1, it.first));

    inputfile.close();
    return 0;
}