#include<bits/stdc++.h>

using namespace std;

struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}init;
#define N 0
#define D 1
#define I 2
typedef long long LL;
typedef vector<LL> V;
typedef vector<V> VV;
typedef vector<VV> VVV;
const LL INF=1e15;
int main(){
    int n,m;
    cin>>n>>m;

    string S,T;
    cin>>S>>T;

    VVV dp(n+1,VV(m+1,V(3,INF)));
    VVV prev(n+1,VV(m+1,V(3,-1)));

    dp[0][0][0]=0;
    for(int i=0;i<=n;i++)
        for(int j=0;j<=m;j++){
            V &now=dp[i][j];
            if(i<n){//Delete
                V &nxt=dp[i+1][j];
                V &p=prev[i+1][j];
                
                if(nxt[D]>now[N]+9){
                    nxt[D]=now[N]+9;p[D]=N;
                }                
                if(nxt[D]>now[I]+9){
                    nxt[D]=now[I]+9;p[D]=I;
                }
                if(nxt[D]>now[D]+2){
                    nxt[D]=now[D]+2;p[D]=D;
                }
            }
            if(j<m){//Insert
                V &nxt=dp[i][j+1];
                V &p=prev[i][j+1];
                
                if(nxt[I]>now[N]+9){
                    nxt[I]=now[N]+9;p[I]=N;
                }                
                if(nxt[I]>now[I]+2){
                    nxt[I]=now[I]+2;p[I]=I;
                }
                if(nxt[I]>now[D]+9){
                    nxt[I]=now[D]+9;p[I]=D;
                }
            }
            if(i<n&&j<m){//Change
                V &nxt=dp[i+1][j+1];
                V &p=prev[i+1][j+1];
                int cost=0;
                if(S[i]!=T[j])cost=5;
                if(nxt[N]>now[N]+cost){
                    nxt[N]=now[N]+cost;p[N]=N;
                }                
                if(nxt[N]>now[I]+cost){
                    nxt[N]=now[I]+cost;p[N]=I;
                }
                if(nxt[N]>now[D]+cost){
                    nxt[N]=now[D]+cost;p[N]=D;
                    }
            }
        }
    LL res=INF;
    int pp=-1;
    for(int i=0;i<3;i++)if(res>dp[n][m][i]){
            res=dp[n][m][i];
            pp=i;
        }
    cout<<res<<endl;
    int s=n;
    int t=m;
    string cmd;
    while(s>0||t>0){
        int np=prev[s][t][pp];
        // cout<<s<<" "<<t<<endl;
        //cout<<dp[s][t][pp]<<endl;
        //cout<<pp<<"  "<<np<<endl;
        if(pp==D){
            s--;
            cmd+="D";
        }
        if(pp==I){
            t--;
            cmd+="I";
        }
        if(pp==N){
            s--,t--;
            cmd+="N";
        }
        pp=np;
    }
    string SS,TT;
    reverse(cmd.begin(),cmd.end());
    s=0,t=0;
    for(auto &it:cmd){
        if(it=='I'){
            SS+='-';
            TT+=T[t++];
        }
        if(it=='D'){
            TT+='-';
            SS+=S[s++];
        }
        if(it=='N'){
            SS+=S[s++];
            TT+=T[t++];
        }
    }
    cout<<SS<<endl;
    cout<<TT<<endl;
    return 0;
}