# Author:  James Tam
# Version: November, 2013

# Learning concepts:
# Using the isdigit string method to verify the type of data.
ok = False
while (ok == False):
   temp = input("Enter an integer: ")
   ok = temp.isdigit()
   if (ok == False):
      print(temp, "is not an integer")
num = int (temp)
num = num + num
print(num)