grep search result + 1 HELP PLEASE!

ok ppl, i have the following problem, i have a lot of dates to manage and sometimes i have to change all of them, for example, 1 day ahead of what i have, so (DD.MM.YYYY) 02.08.2013 has to become 03.08.2013

i came up with this

var myDocument = app.documents.item(0);

//grep search string for the first two digits of this date format: DD.MM.201X

var myString = "\\d\\d(?=\\.\\d+\\.201\\d)";

//empties the search strings

app.findGrepPreferences = NothingEnum.nothing;

app.changeGrepPreferences = NothingEnum.nothing;

//does not perform a search on the following items

app.findChangeGrepOptions.includeFootnotes = false;

app.findChangeGrepOptions.includeHiddenLayers = false;

app.findChangeGrepOptions.includeLockedLayersForFind = false;

app.findChangeGrepOptions.includeLockedStoriesForFind = false;

app.findChangeGrepOptions.includeMasterPages = false;

//searches for the grep string

app.findGrepPreferences.findWhat = myString;

//suposedly adds 1 to the result of the grep search

var add = myDocument.findGrep() + 1;

app.changeGrepPreferences.changeTo = add;

myDocument.changeGrep();

//empties searches again

app.findGrepPreferences = NothingEnum.nothing;

app.changeGrepPreferences = NothingEnum.nothing;

the problem is that it doesnt parse what it finds as integers but as [OBJECT]

so what i get in return is [OBJECT]1.08.2013 instead of adding 1 to the first two digits