#include <bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define ll long long
#define ld double
#define llu long long unsigned

string A , B;

int dp[ (int)1e4 ][ (int)1e4 ];
bool visited[ (int)1e4 ][ (int)1e4 ];

int calcLCS( int  i , int j )
{

    if( A[ i ] == '\0' or B[ j ] == '\0' )
        return 0;

    if( visited[ i ][ j ] )
        return dp[ i ][ j ];

    int ans = 0;

    if( A[ i ] == B[ j ] )
        ans = 1 + calcLCS( i + 1 , j + 1 );

    else
        ans = max( calcLCS( i + 1 , j ) , calcLCS( i , j + 1 ) );

    visited[ i ][ j ] = 1;
    dp[ i ][ j ] = ans;

    return ans;

}

string ansString = "";

void printLCS( int i , int j )
{

    if( A[i] == '\0' or B[j] == '\0' )
    {
         cout<<ansString<<endl;
         return;
    }

    if( A[i] == B[j] )
    {
        ansString += A[i];
        printLCS( i + 1 , j + 1 );
    }

    else if( dp[i+1][j] > dp[i][j+1] )
        printLCS( i + 1 , j );

    else
        printLCS( i , j + 1 );

}

string ansAllString = "";

void printAllLCS( int i , int j )
{

    if( A[i] == '\0' or B[j] == '\0' )
    {
         cout<<ansAllString<<endl;
         return;
    }

    if( A[i] == B[j] )
    {
        ansAllString += A[i];
        printAllLCS( i + 1 , j + 1 );
        ansAllString.erase( ansAllString.size() - 1 , 1 );
    }

    else if( dp[i+1][j] > dp[i][j+1] )
        printAllLCS( i + 1 , j );

    else if( dp[i+1][j] < dp[i][j+1] )
        printAllLCS( i , j + 1 );

    else
        printAllLCS( i + 1 , j ) , printAllLCS( i , j + 1 );

}

int main()
{
    fast;

    cin>>A>>B;
    cout<<calcLCS( 0 , 0 )<<endl;
    printLCS( 0 , 0 );
    printAllLCS( 0 , 0 );

    return 0;
}