code: def lcs(s1, s2, i, j):
      
      if i == 0 or j == 0:
          return 0
      elif s1[i - 1] == s2[j - 1]:
          return 1 + lcs(s1, s2, i - 1, j - 1)
      else:
          return max(lcs(s1, s2, i - 1, j), lcs(s1, s2, i, j - 1))
docs: The length of longest common subsequence among the two given strings s1 and s2