#message to be encrpyted/decrypted 
inputText = 'secret message'
# encryption/decryption key 
key = 5
# encrpyt or decrypt
mode = 'encrypt'
# ledger
ledger = 'abcdefghijklmnopqrstuvwxyz 1234567890'
# output message
outputText = ''
for char in inputText:
#find the index of the character in ledger
inputIndex = ledger.find(char)
# perform ecryption/decryption
if mode == 'encrypt':
outputIndex = inputIndex + key
elif mode 'decrypt':
outputIndex = inputIndex - key
# handle wraparaound
if outputIndex >= len(ledger):
outputIndex = outputIndex - len(ledger)
elif outputIndex < 0:
outputIndex = outputIndex + len(ledger)
# output
outputText = outputText + ledger [outputIndex]

print(outputText)