#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;
using ll = long long;

int main() {
    int n = 26;
    vector<vector<int>> to(n);
    rep(i, n)rep(j, n) {
        to[i].push_back(j);
    }
    
    vector<int> path;
    vector<int> it(n);
    auto dfs = [&](auto& f, int v) -> void {
        while (it[v] < to[v].size()) {
            int u = to[v][it[v]++];
            f(f, u);
        }
        path.push_back(v);
    };
    dfs(dfs, 0);
    
    reverse(path.begin(), path.end());
    
    rep(i, path.size()-1) {
        cout << char('A'+path[i]) << char('A'+path[i+1]) << '\n';
    }
    
    return 0;
}