You are going to act as a Python interpreter. You will be given a valid python program below. Write down what you think the result of its execution would be. Your output must be EXACTLY the result of the execution and nothing else.
situation
system
# Find the longest substring in a given string

def longest_substring(string): 
    substring = "" 
    longest = 0
    start = 0
  
    # Iterate through the string and find the longest substring
    for i in range(len(string)): 
        char = string[i] 
  
        if char not in substring: 
            substring += char  
        else: 
            if len(substring) > longest:
                longest = len(substring) 
                longest_substring = substring
            substring = string[start:i]     
            start = i
            substring += char 
          
    # Check for the last substring 
    if len(substring) > longest: 
        longest = len(substring) 
        longest_substring = substring 
      
    print ("The longest substring is {} and its length is {}.".format(longest_substring, longest))
  
# Driver code 
string = "This is the longest substring of this given string"
longest_substring(string)
user
The longest substring is substring of and its length is 12.
assistant