Buggy python submission (verdict: Time Limit Exceeded):
#float型を許すな
#numpyはpythonで
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
from collections import Counter, deque
from collections import defaultdict
from itertools import combinations, permutations, accumulate, groupby, product
from bisect import bisect_left,bisect_right
from heapq import heapify, heappop, heappush
from math import floor, ceil,pi,factorial
from operator import itemgetter
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))
def LI2(): return [int(input()) for i in range(n)]
def MXI(): return [[LI()]for i in range(n)]
def SI(): return input().rstrip()
def printns(x): print('\n'.join(x))
def printni(x): print('\n'.join(list(map(str,x))))
inf = 10**17
mod = 10**9 + 7
s=SI()
t=SI()
a=len(s)
b=len(t)
dp=[[[0,[]] for j in range(a+1)] for i in range(b+1)]
for i in range(1,b+1):
    for j in range(1,a+1):
        if s[j-1]==t[i-1]:
            dp[i][j][0]=dp[i-1][j-1][0]+1
            for x in dp[i-1][j-1][1]:
                dp[i][j][1].append(x)
            dp[i][j][1].append(j-1)
        else:
            if dp[i-1][j][0]>=dp[i][j-1][0]:
                dp[i][j][1]=dp[i-1][j][1]
            else:
                dp[i][j][1]=dp[i][j-1][1]
            dp[i][j][0]=max(dp[i-1][j][0],dp[i][j-1][0])
for z in dp[-1][-1][1]:
    print(s[z],end="")

#print(dp[-1][-1])
#print(dp)




            

    
    



Fixed submission:
#float型を許すな
#numpyはpythonで
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
from collections import Counter, deque
from collections import defaultdict
from itertools import combinations, permutations, accumulate, groupby, product
from bisect import bisect_left,bisect_right
from heapq import heapify, heappop, heappush
from math import floor, ceil,pi,factorial
from operator import itemgetter
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))
def LI2(): return [int(input()) for i in range(n)]
def MXI(): return [[LI()]for i in range(n)]
def SI(): return input().rstrip()
def printns(x): print('\n'.join(x))
def printni(x): print('\n'.join(list(map(str,x))))
inf = 10**17
mod = 10**9 + 7
s=SI()
t=SI()
a=len(s)
b=len(t)
dp=[[0]*(a+1) for i in range(b+1)]
for i in range(1,b+1):
    for j in range(1,a+1):
        if s[j-1]==t[i-1]:
            dp[i][j]=dp[i-1][j-1]+1
        else:
            dp[i][j]=max(dp[i-1][j],dp[i][j-1])
ans=[]
i,j=b,a
while i > 0 and j > 0:
    if dp[i][j] == dp[i][j-1]:
        j -= 1
    elif dp[i][j] == dp[i-1][j]:
        i -= 1
    else:
        ans.append(s[j-1])
        i -= 1
        j -= 1
#print(ans)
for x in list(reversed(ans)):
    print(x,end="")

Buggy python submission (verdict: Time Limit Exceeded):
#float型を許すな
#numpyはpythonで
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
from collections import Counter, deque
from collections import defaultdict
from itertools import combinations, permutations, accumulate, groupby, product
from bisect import bisect_left,bisect_right
from heapq import heapify, heappop, heappush
from math import floor, ceil,pi,factorial
from operator import itemgetter
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))
def LI2(): return [int(input()) for i in range(n)]
def MXI(): return [[LI()]for i in range(n)]
def SI(): return input().rstrip()
def printns(x): print('\n'.join(x))
def printni(x): print('\n'.join(list(map(str,x))))
inf = 10**17
mod = 10**9 + 7
s=SI()
t=SI()
a=len(s)
b=len(t)
dp=[[[0,""] for j in range(a+1)] for i in range(b+1)]
for i in range(1,b+1):
    for j in range(1,a+1):
        if s[j-1]==t[i-1]:
            dp[i][j][0]=dp[i-1][j-1][0]+1
            dp[i][j][1]=dp[i-1][j-1][1]+s[j-1]
        else:
            dp[i][j]=max(dp[i-1][j],dp[i][j-1])
print(dp[-1][-1][1])
#print(dp)




            

    
    



Fixed submission:
#float型を許すな
#numpyはpythonで
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)
from collections import Counter, deque
from collections import defaultdict
from itertools import combinations, permutations, accumulate, groupby, product
from bisect import bisect_left,bisect_right
from heapq import heapify, heappop, heappush
from math import floor, ceil,pi,factorial
from operator import itemgetter
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))
def LI2(): return [int(input()) for i in range(n)]
def MXI(): return [[LI()]for i in range(n)]
def SI(): return input().rstrip()
def printns(x): print('\n'.join(x))
def printni(x): print('\n'.join(list(map(str,x))))
inf = 10**17
mod = 10**9 + 7
s=SI()
t=SI()
a=len(s)
b=len(t)
dp=[[0]*(a+1) for i in range(b+1)]
for i in range(1,b+1):
    for j in range(1,a+1):
        if s[j-1]==t[i-1]:
            dp[i][j]=dp[i-1][j-1]+1
        else:
            dp[i][j]=max(dp[i-1][j],dp[i][j-1])
ans=[]
i,j=b,a
while i > 0 and j > 0:
    if dp[i][j] == dp[i][j-1]:
        j -= 1
    elif dp[i][j] == dp[i-1][j]:
        i -= 1
    else:
        ans.append(s[j-1])
        i -= 1
        j -= 1
#print(ans)
for x in list(reversed(ans)):
    print(x,end="")