s1, s2 = input(), input()
l1, l2 = len(s1), len(s2)
dp = [[0]*(l2+1) for _ in range(l1+1)]

for i in range(l1) :
    for j in range(l2) :
        if s1[i] == s2[j] :
            dp[i+1][j+1] = dp[i][j] + 1
        else :
            dp[i+1][j+1] = max(dp[i+1][j], dp[i][j+1])

print(dp[l1][l2])

if dp[l1][l2] != 0 :
    ans = []
    p1, p2 = l1, l2
    
    while p1 > 0 and p2 > 0 :
        if dp[p1][p2-1] == dp[p1][p2] :
            p2 -= 1
        elif dp[p1-1][p2] == dp[p1][p2] :
            p1 -= 1
        else :
            ans.append(s2[p2-1])
            p1, p2 = p1-1, p2-1

    print("".join(ans[::-1]))