NEW YORK (AP) — With the protest on Wall Street entering its fourth week, police officers are keeping their posts surrounding the park at the center of it all as the Occupy Wall Street demonstrators say they are staying put for the long haul.

“The bottom line is that people want to express themselves, and as long as they obey the laws, we allow them to,” Mayor Michael Bloomberg told reporters Monday when asked about the protesters’ staying power. “If they break the laws, then we’re going to do what we’re supposed to do — enforce the laws.”

The protesters say they’re fighting for the “99 percent,” or the vast majority of Americans who do not fall into the wealthiest 1 percent of the population; their causes range from bringing down Wall Street to fighting global warming. The movement gained traction through social media, and protests have taken place in several other cities nationwide.

On Monday, the Rev. Al Sharpton and rapper Kanye West made impromptu appearances at the park. A march was planned for Monday evening, though details were unclear. A group of mothers also brought small children downtown to teach them about the movement, calling themselves the “99 Percent School.”

In Boston, hundreds of college students marched through downtown Monday and gathered on Boston Common, holding signs that read “Fund education, not corporations.” The protesters said they’re angry with an education system they say mimics what they call the “irresponsible, unaccountable, and unethical financial practices” of Wall Street.

In New York, officers from the city’s First Precinct are patrolling the area near Wall Street, and other squads help out as necessary, depending on the size and movement of the demonstrators. If the crowd seems to be growing on a particular day, the NYPD dispatches more officers to the area, Police Commissioner Raymond Kelly said.

There are many events in New York City that require a police presence, like parades, said James Parrott, deputy director and chief economist for the Fiscal Policy Institute.

The NYPD has already spent $1.9 million, mostly in overtime pay, to patrol the area near Zuccotti Park, where hundreds of protesters have camped out for several weeks.

By comparison, it cost about $50 million for one week to secure the Republican National Convention in 2004, which included massive protests and other events around the city.

“To some extent this sort of thing happens a lot in New York City,” Parrott said. ”$2 million in the context of a $66 billion annual budget is not a deal breaker.”

Most of the protesters seem to share that view. Mark Bray, a spokesman for the protesters who was working the media table at Zuccotti Park on Monday, questioned the need for such a strong police presence in the first place.

“If your argument is that police expense equals an ineffective message, how are you ever going to form a movement?” he said. “Because the police always come out, you know?”

Copyright 2011 The Associated Press.