Discrete mathematics problem!!?

John and Sara gave a party that was attended by n married couples. As the guests arrived, some shook hands with their host or hostess or with other guests who had arrived earlier. When all the guests were embled, John asked and also Sara how many hands each had shaken. He discovered that everyone gave a different answer. uming that no guests shook their own hands or the hands of their spouses, how many hands did Sara shake? Prove your answer by mathematical induction.