using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Diagnostics;
using Enu = System.Linq.Enumerable;

public class Program
{
    int N, M;
    string S, T, X = "", Y = "";
    int?[, ,] MinCost;

    public void Solve()
    {
        N = Reader.Int(); M = Reader.Int();
        S = Reader.String(); T = Reader.String();
        MinCost = new int?[N + 1, M + 1, 3];
        int ans = Rec(0, 0, 0, 0);
        Console.WriteLine(ans + "\n" + X + "\n" + Y);
        Console.ReadLine();
    }

    private int Rec(int si, int ti, int type, int gen = 0)
    {
        if (si == N && ti == M) return 0;
        if (gen == 0 && MinCost[si, ti, type].HasValue) return MinCost[si, ti, type].Value;
        int cost = int.MaxValue, bestType = 0;

        if (si < N && ti < M)
            cost = (S[si] == T[ti] ? 0 : 5) + Rec(si + 1, ti + 1, 0);
        if (ti < M && CheckMin(ref cost, (type == 1 ? 2 : 9) + Rec(si, ti + 1, 1)))
            bestType = 1;
        if (si < N && CheckMin(ref cost, (type == 2 ? 2 : 9) + Rec(si + 1, ti, 2)))
            bestType = 2;

        if (si + ti == 0 || gen == 1)
        {
            if (bestType == 0) { X += S[si]; Y += T[ti]; Rec(si + 1, ti + 1, 0, 1); }
            if (bestType == 1) { X += "-"; Y += T[ti]; Rec(si, ti + 1, 1, 1); }
            if (bestType == 2) { X += S[si]; Y += "-"; Rec(si + 1, ti, 2, 1); }
        }
        MinCost[si, ti, type] = cost;
        return cost;
    }

    bool CheckMin(ref int a, int b) { if (b < a) { a = b; return true; } return false; }
}

class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    static TextReader reader = Console.In;
    static readonly char[] separator = { ' ' };
    static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    static string[] A = new string[0];
    static int i;
    static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Range(N, Int); }
    public static int[][] IntTable(int H) { return Range(H, IntLine); }
    public static string[] StringArray(int N) { return Range(N, Next); }
    public static string[][] StringTable(int N) { return Range(N, () => Split(Line())); }
    public static string Line() { return reader.ReadLine().Trim(); }
    static string[] Split(string s) { return s.Split(separator, op); }
    static T[] Range<T>(int N, Func<T> f) { var r = new T[N]; for (int i = 0; i < N; r[i++] = f()) ; return r; }
    static string Next() { CheckNext(); return A[i++]; }
    static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}