I always thought like that:

Hmmm: 1 + 2 + 3 + ... + 99 + 100

Kommutativgesetz be like: This equals:
100 +1 + 99 + 2 +98 + 3 . . . And this equals: 101+ 101+ 101+ . . .

How often do I need to do this? I use up 2 numbers for each 101. I have 100 numbers total. So that's 50x101.

Now you can think about: What if it's 1000 instead of 100? But it#s easy from here...