Birthday Party!

Sejal wants to have a get-together with her friends, as she had had last year. She has n friends and each of them came to her house and stayed for a specific range of days of the year from si(start date) to ei(end date), the previous year. Last year, all the people who met each other became friends and had exchanged their contact details. Person A met Person B, if and only if Person A's start date