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Hundreds of thousands of Brazilians peacefully marched Sunday in over 50 cities around the country to demand President Dilma Rousseff's impeachment and to criticize government corruption.

Police estimated 15,000 people marched along the golden sands of Copacabana beach in Rio de Janeiro, where they waved Brazilian flags and many openly called for a military coup to dissolve the government.

"I don't want my country to turn into a Venezuela, we don't want an authoritarian government!" said Marlon Aymes, 35, helping carry a 20-foot long banner that read in English: "Army, Navy and Air Force. Please Save Us Once Again of Communism."

"We want the military to dissolve Congress and call new elections, because the level of corruption is too widespread to do anything else," Aymes added.

The biggest protests were in Sao Paulo, an opposition stronghold where hundreds of thousands gathered on a main avenue, as well as in the capital city Brasilia and Rio. Dozens of cities saw demonstrations gathering together a few thousand people each. According to the website of the Globo TV network, Brazil's largest, the total number in the streets across Brazil was over 300,000 people, based on local police estimates.

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Much protester ire was focused on a kickback scheme at state-run oil company Petrobras, which prosecutors call the biggest corruption scheme ever uncovered in Brazil. At least $800 million was paid in bribes and other funds by the nation's biggest construction and engineering firms in exchange for inflated Petrobras contracts.

Top executives are already in jail and the attorney general is investigating dozens of top congressmen, along with current and former members of the executive branch, for alleged connections to the scheme that apparently began in 1997 before Rousseff's party took power in 2003. Rousseff, a former chairwoman of Petrobras' board, has not been implicated and so far is not being investigated, though top officials from her administration, including two former chiefs of staff, are caught up in the inquiry.

The marches add pressure on Rousseff, whose poll ratings have never been lower and who is facing duel economic and political crises. But the protests are significantly different than anti-government demonstrations in 2013. Those earlier protests cut across political, social and economic lines, and were a widespread expression of frustration with poor public services like health care and transportation, as well as a cry against government corruption.

Sunday's protests, largely organized by ad-hoc right-leaning groups over social media, appeared far more politically focused, and demonstrators came from social classes that voted against Rousseff in her narrow re-election in October.

Despite their partisan nature, the mass marches are another thorn in Rousseff's side. They also add impetus to opposition efforts to thwart measures she backs in Congress, where even those in the ruling Workers' Party coalition are creating hurdles as she tries to push through austerity measures.

Brazilian growth has been weak since Rousseff took office in 2011. The country likely entered a recession in 2014 and most economists surveyed by the Central Bank forecast negative growth for this year. Inflation is rising and the local currency has plummeted against the dollar in recent weeks, making life more expensive in a nation with a surprisingly high cost of living and one of the world's heaviest tax burdens.

Still, Brazil's top opposition political figures, including a former president and the top candidates who ran against Rousseff in last year's election, say impeachment is undesirable, because the president isn't accused of any connection to the Petrobras scandal, and because it could affect Brazil's stability.

Pedro Arruda, a political scientist at the Pontifical Catholic University in Sao Paulo, said demonstrators have the right to demand Rousseff's ouster, "but the impeachment they ... demand has no legal foot to stand on."

"The accumulated feelings of frustration, disappointment and discontent will fuel the demonstrations, but cannot be used to justify calls for her impeachment," Arruda said.

At Copacabana beach, protester Sheila Alcantara said she was angry she had to recently close a restaurant she owned because of rapidly rising prices for electricity and food.

"Never in my life have I heard of so much corruption, of so much money lost," she said. "A military intervention is the only way to clean the government, the executive branch cabinet, the Congress. They're all bribed off."

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