I will travel to Israel from Lisbon in August and I will spent around 1 year there. I will do voluntary work there and the organization that I will serve for told me that a round trip ticket is necessary to travel to Israel. They told me that depending on the airline company I may buy a ticket with a flexibility in the return date.

What would be the best thing to do in this situation, knowing that I will departure in August and return around a year later?