#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back
#define pcnt __builtin_popcount
#define show(x) cout<<#x<<" = "<<x<<endl;
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define fi first
#define se second
#define rng(a) a.begin(),a.end()
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define sz(x) (int)(x).size()
#define mp make_pair

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef set<int> si;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<pll> vpll;
typedef set<ll> sl;
typedef __int128_t lll;
typedef pair<lll,lll> plll;
typedef vector<lll> vlll;
template<typename T>string join(vector<T>&v)
{stringstream s;FOR(i,0,sz(v))s<<' '<<v[i];return s.str().substr(1);}
ll gcd(ll a,ll b){if(a>b)swap(a,b);for(;a>0;b%=a,swap(a,b));return b;}
int modpow(ll a,ll n,int m){if(a==0)return a;ll p=1;for(;n>0;n/=2,a=a*a%m)if(n&1)p=p*a%m;return(int)p;}
void dout(double d){printf("%.12f\n",d);}

const int iinf = 1e9;
const ll linf = 1e18;
const int mod = 1e9+7;
const double pi = acos(-1);
const double eps = 1e-10;
int n, m;
pii DP[1201][1201][3];
string s, t;

main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m >> s >> t;
  pii imp = mp(iinf, -1);

  fill(DP[0][0], DP[1021][0], imp);

  DP[0][0][0] = mp(0, -1);
  int c;
  FOR(i, 0, n+1)FOR(j, 0, m+1){
    if((i==0)&&(j==0)) continue;
    if((i > 0) && (j > 0)){
      c = s[i-1] == t[j-1] ? 0 : 5;
      mins(DP[i][j][0], mp(DP[i-1][j-1][0].fi + c, 0));
      mins(DP[i][j][0], mp(DP[i-1][j-1][1].fi + c, 1));
      mins(DP[i][j][0], mp(DP[i-1][j-1][2].fi + c, 2));
    }
    if(i > 0){
      mins(DP[i][j][1], mp(DP[i-1][j][0].fi + 9, 0));
      mins(DP[i][j][1], mp(DP[i-1][j][1].fi + 2, 1));
      mins(DP[i][j][1], mp(DP[i-1][j][2].fi + 9, 2));
    }
    if(j > 0){
      mins(DP[i][j][2], mp(DP[i][j-1][0].fi + 9, 0));
      mins(DP[i][j][2], mp(DP[i][j-1][1].fi + 9, 1));
      mins(DP[i][j][2], mp(DP[i][j-1][2].fi + 2, 2));
    }
  }
  int ans = iinf, idx;
  FOR(i, 0, 3)if(ans > DP[n][m][i].fi){
    ans = DP[n][m][i].fi;
    idx = i;
  }
  cout << ans << endl;
  int _n = n, _m = m, _idx;
  vector<char> vs, vt;
  while(idx != -1){
    _idx = DP[_n][_m][idx].se;
    switch(idx){
      case 0:
        vs.pb(s[_n-1]);
        vt.pb(t[_m-1]);
        _n--;
        _m--;
        break;
      case 1:
        vs.pb(s[_n-1]);
        vt.pb('-');
        _n--;
        break;
      case 2:
        vs.pb('-');
        vt.pb(t[_m-1]);
        _m--;
        break;
      default:
        break;
    }
    idx = _idx;
  }
  reverse(rng(vs));
  reverse(rng(vt));
  each(itr, vs)cout << *itr;
  cout << endl;
  each(itr, vt)cout << *itr;
  cout << endl;
  return 0;
}