memo=[[0]*(len(s2)+1) for _ in range((len(s1)+1))]        
    for i in range(1, len(s1)+1):
        for j in range(1, len(s2)+1):          
            if s1[i-1]==s2[j-1] :          
                memo[i][j]=memo[i-1][j-1]+1
            else:
                memo[i][j]=max(memo[i-1][j], memo[i][j-1])
                                
    _cur=memo[-1][-1]
    suffixes=[[0]*(len(s2)+1) for _ in range((len(s1)+1))] 
    print(memo)      
    for i in range(len(s1)-1, -1, -1):
        for j in range(len(s2)-1, -1, -1):
            print(s1[i], s2[j])
            if s1[i]==s2[j]:   
                suffixes[i][j]=suffixes[i+1][j+1]+1
            else:
                suffixes[i][j]=max(suffixes[i+1][j], suffixes[i][j+1]) 
    count=0
    print(suffixes)
    for i in range(len(s1)+1):
        seen=set()
        for j in range(len(s2)):
            if memo[i][j]+suffixes[i][j+1]+1>_cur:
                count+=1
                seen.add(s2[j])
    return count