Simple function calling doesn't work in Robot Framework

I'm new to Robot FW and I'm in the learning stage. In order to try calling external libraries, I made a very simple function and saved in tryingLibrary.py file. The content:

def myAdding(x, y):
    z = x + y
    return z

Then I worte the following RF test

*** Settings ***
Documentation    Suite description
Library          tryingLibrary.py

*** Variables ***
${x}

*** Test Cases ***
TestTest
    ${x}=  myAdding     30      26

However, when I check the log file, I find ${x} = 3026. I mean I'm expecting of course 56 not 3026

So where might be the problem?