R, 2213 bytes
catsum(scan(n=2),sep="1"+1)
Takes exactly 2 numbers as the input, and outputs both of them sticked together, thus creating a new natural number.
The n=2 adds 3 bytes and is perhaps unecessary, if the user knows howThanks to stop the scan functionJonathan Allan for his inputs (i.e. by giving a blank line as the input).!