Boulder, Colo. -- Police at the University of Colorado said they didn't write a single ticket at this year's annual marijuana smoke-in on campus.

The so-called 4/20 celebration drew about 10,000 smokers to the Boulder campus and went off without any major hitches or arrests.

The Colorado Daily Camera said Monday that this year's event was different from other years when the campus police photographed participants and sent out citations after they were positively identified.

"There's no way our 12 to 15 officers are going to be able to deal with a crowd of 10,000," conceded Police Cmdr. Brad Wiesely. "We just can't do strong enforcement when we're outnumbered 700 or 800 to one."

Police were reinforced by Boulder County sheriff's deputies and handled four calls related to medical problems, the newspaper said.

Copyright 2008 by United Press International.