#include<bits/stdc++.h>
using namespace std;

#define int long long
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}


int N,M;
string S,T;


int dp[1201][1201][3];
tuple<int,int,int>pre[1201][1201][3];
void a(int i,int j,int k,int ii,int jj,int kk,int c){
    if(dp[i][j][k]>=dp[ii][jj][kk]+c){
        dp[i][j][k]=dp[ii][jj][kk]+c;
        pre[i][j][k]=make_tuple(ii,jj,kk);
    }
}
signed main(){
    cin>>N>>M;
    cin>>S>>T;

    fill_n(**dp,1201*1201*3,1001001001001001001ll);
    dp[0][0][0]=0;
    for(int i=0;i<=N;i++){
        for(int j=0;j<=M;j++){
            if(i<N){
                a(i+1,j,1,i,j,1,2);
                a(i+1,j,0,i,j,1,2);
                a(i+1,j,1,i,j,0,9);
                a(i+1,j,0,i,j,0,9);
            }
            if(j<M){
                a(i,j+1,2,i,j,2,2);
                a(i,j+1,0,i,j,2,2);
                a(i,j+1,2,i,j,0,9);
                a(i,j+1,0,i,j,0,9);
            }
            if(i<N&&j<M){
                a(i+1,j+1,0,i,j,0,S[i]==T[j]?0:5);
            }
        }
    }

    cout<<dp[N][M][0]<<endl;
    string SS,TT;
    int i=N,j=M,k=0;
    while(i>0||j>0){
        int ii,jj,kk;
        tie(ii,jj,kk)=pre[i][j][k];

        if(ii<i&&jj<j){
            SS+=S[ii];
            TT+=T[jj];
        }
        else if(ii<i){
            SS+=S[ii];
            TT+='-';
        }
        else if(jj<j){
            SS+='-';
            TT+=T[jj];
        }
        i=ii;j=jj;k=kk;
    }

    reverse(all(SS));reverse(all(TT));
    cout<<SS<<endl;
    cout<<TT<<endl;
    return 0;
}