You are given a positive integer X. Write a simple program to find the second largest digit in the given number X.

Sure, here is a simple Python program that finds the second largest digit in a given positive integer X:

def second_largest_digit(X):
    # Convert the integer into a list of its digits
    digits = [int(d) for d in str(X)]
    
    # Sort the list in descending order
    digits.sort(reverse=True)
    
    # Remove the largest digit
    digits.remove(digits[0])
    
    # The second largest digit is now the first element in the list
    second_largest = digits[0]
    
    return second_largest

# Test the function
X = 123456789
print(second_largest_digit(X))  # Output: 8

This program works by first converting the integer into a list of its digits. It then sorts this list in descending order and removes the largest digit. The second largest digit is now the first element in the list.