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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    vector<vector<int>> B(26, vector<int>(26, -1));
    vector<string> ans;
    auto dfs = [&](auto dfs, char v, char p) -> void{
        if(p != '-') ans.emplace_back(string(1, p) + string(1, v));
        for(int i = 0; i < 26; i++){
            if(B[v - 'A'][i] != -1) continue;
            B[v - 'A'][i] = 0;
            dfs(dfs, i + 'A', v);
        }
    };
    dfs(dfs, 'A', '-');
    for(auto &&ss : ans) cout << ss << '\n';
}