By Angeliki Koutantou ATHENS (Reuters) - Several thousand demonstrators chanting "Europe! Europe!" rallied in front of parliament in Athens on Thursday calling for Greece to keep the euro, as the country edged nearer to a default that could force it out of the single currency zone. Greece's future in the bloc and even in the EU has hung in the balance as the leftist government of Prime Minister Alexis Tsipras, which swept to power five months ago on a platform of resisting austerity, has reached deadlock with its creditors. "This is the first demonstration I've joined in for the last five years because it's the first time that we've been at risk of quitting the euro," said Alexandra Spei, a 50-year-old accountant.