如题。

#2: Wrong Answer.wrong answer On line 1 column 1, read *, expected w.

#3: Wrong Answer.wrong answer On line 1 column 11, read s, expected k.

#6: Wrong Answer.wrong answer On line 1 column 2, read e, expected b.

#7 ~ #10: RE

#include <bits/stdc++.h>
typedef long long ll;

const int Al = 30;
struct node {
	int to; std::string str;
	bool operator < (const node &cmp) const {
		if (str.length() < cmp.str.length()) return str.length() < cmp.str.length();
		for (int i = 0; i < str.length(); ++ i) if (str[i] < cmp.str[i]) return 1;
		return 0;
	}
}; std::vector <node> G[Al]; // to save the graph

int n;
int in[Al], out[Al], anc[Al];
int find(int u) {
	if (anc[u] == u) return u;
	else return anc[u] = find(anc[u]);
} 
void merge(int u, int v) {
	anc[find(u)] = find(v);
	return void();
}
int Jud() {
//	if it's not connected
	for (int i = 1; i <= 26; ++ i) anc[i] = i;
	int flag = 0; 
	for (int i = 1; i <= 26; ++ i)
		for (int j = 0; j < G[i].size(); ++ j) if (find(i) != find(G[i][j].to)) merge(i, G[i][j].to), flag = i;
//	for (int i = 1; i <= 26; ++ i) std::cout << find(i) << " ";
	for (int i = 1; i <= 26; ++ i) if ((in[i] || out[i]) && find(i) != find(flag)) return -1; 
	
//	std::cout << "here\n";
	
//	if it's not an Euler Graph
	int cnt = 0;
	for (int i = 1; i <= 26; ++ i) cnt += (in[i] == out[i]);
	if (cnt != 26 && cnt != 24) return -1;
	
	if (cnt == 26) {
		int fl = 0;
		for (int i = 1; i <= 26; ++ i) if (in[i] || out[i]) return i;
	}
	if (cnt == 24) {
		int c1 = 0, c2 = 0; 
		for (int i = 1; i <= 26; ++ i) c1 += (in[i] - out[i] == 1), c2 += (out[i] - in[i] == 1);
		if (! (c1 == 1 && c2 == 1)) return -1;
		
//		std::cout << c1 << " " << c2 << "\n";
		
		for (int i = 1; i <= 26; ++ i) if (out[i] - in[i] == 1) return i;
	}
}

int del[Al];

std::vector <std::string> ans;
void dfs(int u) {
	for (; del[u] < G[u].size(); ) {
		int v = G[u][del[u]].to;
		std::string str = G[u][del[u]].str;
		++ del[u];
		dfs(v);
		ans.push_back(str);
	}
	return void();
}

int main() {

//	freopen(".in", "r", stdin);
//	freopen(".out", "w", stdout);

	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::cout.tie(nullptr);

	std::cin >> n;
	for (int i = 1; i <= n; ++ i) {	
		std::string str = "";
		std::cin >> str;
		int u = str[0] - 'a' + 1, v = str[str.length() - 1] - 'a' + 1;
		G[u].push_back((node) {v, str});
		++ in[v]; ++ out[u];
	}
	
//	for (int i = 1; i <= 26; ++ i) std::cout << in[i] << " " << out[i] << "\n";
	
	int s = Jud(); // start from s
	if (s == -1) return std::cout << "***\n", 0;
	
//	std::cout << s << "\n";
	
	for (int i = 1; i <= 26; ++ i) std::sort(G[i].begin(), G[i].end());
	dfs(s);
	for (int i = ans.size() - 1; i; -- i) std::cout << ans[i] << ".";
	std::cout << ans[0] << "\n";
	
	

	return 0;
}