UVa Q200

//UVa Q200
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#include <bits/stdc++.h>
using namespace std;

bool rec[26][26];//arr[a][b] := a > b
vector<int> v[26];
bool used[26];
void func(string s1, string s2){
    for(unsigned i = 0; i < min(s1.size(), s2.size()); ++i){
        used[s1[i] - 'A'] = used[s2[i] - 'A'] = 1;
        if(s1[i] == s2[i])continue;
        if(!rec[s1[i] - 'A'][s2[i] - 'A'])v[s1[i] - 'A'].emplace_back(s2[i] - 'A');
        rec[s1[i] - 'A'][s2[i] - 'A'] = 1;
        break;
    }
}

vector<int> ans;
int n;
void dfs(int u){
    ans.emplace_back(u);
    if(ans.size() == n)return;
    for(unsigned i = 0; i < v[u].size(); ++i){
        dfs(v[u][i]);
        if(ans.size() == n)return;
    }
    ans.pop_back();
}

int main(){
    string s[2];
    cin >> s[1];
    bool b = 0;
    while(cin >> s[b]){
        if(s[b] == "#")break;
        func(s[!b], s[b]);
        b = !b;
    }
    for(int i = 0; i < 26; ++i)if(used[i])++n;
    for(int i = 0; i < 26; ++i){
        if(used[i])dfs(i);
        if(ans.size() == n)break;
    }
    for(int i = 0; i < ans.size(); ++i){
        cout << char(ans[i]+'A');
    }
    cout << '\n';
    return 0;
}