new_contents: def issubstring(s1,s2):
      #check if s1 is substring of s2
      M = len(s1)
      N = len(s2)
  
      for i in range(N-M+1):
          for j in range(M):
              if s2[i+j] != s1[j]:
                  break
              if j+1 == M:
                  return i 
      return -1
  
  if __name__ == "__main__":
      s1 = "ford"
      s2 = "avfordc"
      print(issubstring(s1,s2))
  
subject: Create isSubstring.py