#include <bits/stdc++.h>

using namespace std;

int Pos[256], Cnt[256];
vector<char> chars;
vector<int> Positions;
string Sol, str;
vector<string> Words;

int main() {
	while(cin >> str) {
		Words.push_back(str);
	}

	for(char c = 'a'; c <= 'z'; ++c) chars.push_back(c);
	for(char c = 'A'; c <= 'Z'; ++c) chars.push_back(c);
	int p = 0;
	for(auto c : chars) Pos[c] = p++;
	Positions.resize(Words.size(), 0);

cerr << "OK\n";


	for(int i = 1; i <= 1e6; ++i) {
	

		memset(Cnt, 0, sizeof(Cnt));
		for(int i = 0; i < Words.size(); ++i) {
			if(Positions[i] < Words[i].size()) {
				char now = Words[i][Positions[i]];
				Cnt[Pos[now]] += 1;
			}
		}

		int best = 0;
		for(int i = 1; i < chars.size(); ++i)
			if(Cnt[best] < Cnt[i])
				best = i;

		if(Cnt[best] == 0) break;

		Sol += chars[best];

		for(int i = 0; i < Words.size(); ++i) {
			if(Positions[i] < Words[i].size()) {
				char now = Words[i][Positions[i]];
				if(Pos[now] == best) ++ Positions[i];
			}
		}
	}

	cout << Sol;


	return 0;
}