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

ifstream fin("cmlsc.in");
ofstream fout("cmlsc.out");

int dp[1005][1005];

int main() {
    string s, t;
    fin >> s >> t;

    int n = s.size();
    int m = t.size();

    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (s[i-1] == t[j-1])
                dp[i][j] = dp[i-1][j-1] + 1;
            else
                dp[i][j] = max(dp[i-1][j], dp[i][j-1]);
        }
    }
    
    string lcs = "";
    int i = n, j = m;

    while (i > 0 && j > 0) {
        if (s[i-1] == t[j-1]) {
            lcs += s[i-1];
            i--; j--;
        } else if (dp[i-1][j] > dp[i][j-1]) {
            i--;
        } else {
            j--;
        }
    }

    reverse(lcs.begin(), lcs.end());

    fout << dp[n][m] << '\n';
    fout << lcs << '\n';

    return 0;
}