Gain For Grabs

upon reaching 0.5 ETH, winner 1 will be chosen (approximately 0.5 ETH prize)
upon reaching 1 ETH, winner 2 will be chosen (approximately 0.5 ETH prize)
upon reaching 2 ETH, winner 3 will be chosen (approximately 1 ETH prize)
upon reaching 4 ETH, winner 4 will be chosen (approximately 2 ETH prize)
upon reaching 8 ETH, winner 4 will be chosen (approximately 4 ETH prize)
and so on, doubling the prize each time