encrypt_file(1)

def encrypt_file(file_name, key):
    with open(file_name, 'r') as file:
        plaintext = file.read()
    
    encrypted_text = encrypt_text(plaintext, key)
    
    with open(f"encrypted_{file_name}", 'w') as file:
        file.write(encrypted_text)
    
    print(f"File '{file_name}' encrypted successfully.")

def decrypt_file(file_name, key):
    with open(file_name, 'r') as file:
        encrypted_text = file.read()
    
    decrypted_text = decrypt_text(encrypted_text, key)
    
    with open(f"decrypted_{file_name}", 'w') as file:
        file.write(decrypted_text)
    
    print(f"File '{file_name}' decrypted successfully.")

def encrypt_text(text, key):
    encrypted_text = ""
    for char in text:
        if char.isalpha():
            if char.isupper():
                encrypted_char = chr((ord(char) - 65 + key) % 26 + 65)
            else:
                encrypted_char = chr((ord(char) - 97 + key) % 26 + 97)
            encrypted_text += encrypted_char
        else:
            encrypted_text += char
    return encrypted_text

def decrypt_text(text, key):
    decrypted_text = ""
    for char in text:
        if char.isalpha():
            if char.isupper():
                decrypted_char = chr((ord(char) - 65 - key) % 26 + 65)
            else:
                decrypted_char = chr((ord(char) - 97 - key) % 26 + 97)
            decrypted_text += decrypted_char
        else:
            decrypted_text += char
    return decrypted_text

def main():
    file_name = input("Enter the file name: ")
    key = int(input("Enter the encryption/decryption key: "))
    mode = input("Enter 'e' to encrypt or 'd' to decrypt: ")

    if mode == 'e':
        encrypt_file(file_name, key)
    elif mode == 'd':
        decrypt_file(file_name, key)
    else:
        print("Invalid mode. Please enter 'e' or 'd'.")

main()