class Solution:
    def longestCommonSubsequence(self, a: str, b: str) -> int:
        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])
        return dp[-1][-1]