a="aa"
b="a"
n=len(a)
m=len(b)
dp=[[0]*(m+1)for i in range(n+1)]
for i in range(1,n+1):
    for j in range(1,m+1):
        if a[i-1]==b[j-1]:
            dp[i][j]=1+dp[i-1][j-1]

        else:
            dp[i][j]=max(dp[i-1][j],dp[i][j-1])
print(dp)