Abaqus, response spectrum analysis

Hi all,

I need to include missing mass method in response spectrum analysis. I found in documentation that I should add the following instruction to my input file:

*RESPONSE SPECTRUM, MISSING MASS METHOD

I tried to put this instruction inside and outside of *step block, but in both cases I got "keyword is misplaced" error. Has anyone encountered such a problem? I would be grateful if someone could send an example of a correct input file.