input: def find_lcs(x: str, y: str) -> str:
      """
      Given two strings, this function finds the longest common subsequence (LCS) of the two strings.
  
      >>> find_lcs("abcdaf", "acbcf")
      'abcf'
      """
output:     m, n = len(x), len(y)
      dp = [[""] * (n + 1) for _ in range(m + 1)]
      
      for i in range(1, m + 1):
          for j in range(1, n + 1):
              if x[i - 1] == y[j - 1]:
                  dp[i][j] = dp[i - 1][j - 1] + x[i - 1]
              else:
                  dp[i][j] = max(dp[i - 1][j], dp[i][j - 1], key=len)
      
      return dp[m][n]