#include<cstdio>
#include<iostream>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
typedef long long ll;int l, n, tot, fail[105], go[105][30];
char s[15], stak[15];
ll dp[105][30][1<<10];
vector<int> G[105];void Add(int x)
{int now = 0;int len = strlen(s);for(int i = 0; i < len; ++i){if(!go[now][s[i]-'a'])go[now][s[i]-'a'] = ++tot;now = go[now][s[i]-'a'];}G[now].push_back(x);
}queue<int> q;void Getfail()
{for(int i = 0; i < 26; ++i)if(go[0][i])q.push(go[0][i]);while(!q.empty()){int st = q.front();q.pop();for(int i = 0 ; i < 26; ++i)if(go[st][i]){q.push(go[st][i]);int t = fail[st];while(t && !go[t][i])   t = fail[t];fail[go[st][i]] = go[t][i];for(unsigned int j = 0; j < G[go[t][i]].size(); ++j){int id = G[go[t][i]][j];G[go[st][i]].push_back(id);}}elsego[st][i] = go[fail[st]][i];}
}ll dfs(int x, int rest, int stu)
{if(dp[x][rest][stu] != -1)  return dp[x][rest][stu];if(rest == 0){if(stu == (1<<n) - 1)return dp[x][rest][stu] = 1;elsereturn dp[x][rest][stu] = 0;}ll ret = 0;for(int i = 0; i < 26; ++i){int to = go[x][i];int nxt = stu;for(unsigned int j = 0; j < G[to].size(); ++j){int id = G[to][j];nxt |= (1<<(id-1));}ret += dfs(to, rest - 1, nxt);}return dp[x][rest][stu] = ret;
}void write(int x, int rest, int stu)
{if(rest == 0){printf("%s", stak+1);printf("\n");return;}for(int i = 0; i < 26; ++i){int to = go[x][i];int nxt = stu;for(unsigned int j = 0; j < G[to].size(); ++j){int id = G[to][j];nxt |= (1<<(id-1));}if(dp[to][rest-1][nxt] > 0){stak[l-rest+1] = i + 'a';write(to, rest - 1, nxt);}}
}int main()
{scanf("%d%d", &l, &n);for(int i = 1; i <= n; ++i){scanf("%s", s);Add(i);}Getfail();memset(dp, -1, sizeof(dp));dfs(0, l, 0);printf("%lld\n", dp[0][l][0]);if(dp[0][l][0] <= 42)write(0, l, 0);return 0;
}