#include <bits/stdc++.h>

using namespace std;

typedef long long tint;

#define forsn(i, s, n) for(int i=s;i<int(n);i++)
#define forn(i, n) forsn(i, 0, n)
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(), v.rend()
#define NACHO ios::sync_with_stdio(0); cin.tie(NULL);

const int INF = 1e6;
const int MOD = 1e9+7;

int t[503][26];
int fin[503];

int depth[503];

int maxi = 0;
string best = "";
string a="";

void dfs(int node=0, int d=0){
    depth[node]+=fin[node];
    forn(i, 26){
        if(t[node][i] != -1){
            a+=(char)('a'+i);
            dfs(t[node][i], d+1);
            depth[node]+=depth[t[node][i]];
        }
    }
    if(d*d*depth[node] > maxi){
        maxi = d*d*depth[node];
        best = a;
    }
    a.pop_back();
}

int main(){
    //ifstream cin("equipo.in");
    //ofstream cout("equipo.out");
    int sz; cin >> sz;
    int n; cin >> n;
    forn(i, 501){
        forn(j, 26){
            t[i][j]= -1;
        }
    }
    int m = 1;
    forn(i, n){
        string s;
        cin >> s;
        int u=0;
        for(char d : s) {
            if(t[u][d-'a'] == -1)
                t[u][d-'a']=m++;
            u=t[u][d-'a'];
        }
        ++fin[u];
    }
    dfs();
    cout << maxi << "\n";
    cout << best << "\n";
}