#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    array<array<bool,26>,26> B{};
    vector<string> ans;
    auto dfs = [&](auto&& dfs, int v) -> void {
        for (int to = 0; to < 26; to++) {
            if (B[v][to]) continue;
            B[v][to] = true;
            dfs(dfs, to);
            ans.push_back(string(1, v + 'A') + string(1, 'A' + to));
        }
    };
    dfs(dfs, 0);
    reverse(ans.begin(), ans.end());
    for (const string& s : ans) cout << s << '\n';
}