Resident Evil 4: Keyboard Controls

Hello.

So, I recently got Resident Evil 4 on PC and I'm stuck because of the controls with the keyboard...

At the beginning of the game, you have to run to avoid getting crushed by a huge boulder thrown by three guys. Running isn't the problem, but I can't manage to dodge the boulder. The screen tells us to press 1 and 3 or 5 and 6, but nothing happens and I get crushed.

I've tried the following keys:

"1" and "3"
"5" and "6"

"Left Shift" and "Right Shift" (for 5 and 6)

"Enter" and "Right Ctrl" (for 1 and 3)

How should I press the keys? Should I hold them down once or click very quickly and simultaneously on both keys as instructed?

Please help me, I'm starting to go crazy with this boulder.

Thanks in advance for your advice.

S.

Configuration: Vaio VGN-FZ38M + Vista WinDVD BD for Vaio