Some hint:
For n = 4

1 : (1,2), (1,3), (1,4);
2 : (2,1), (2,3);
3 : (3,1), (3,2);
4 : (4,1);

1st have 3 friends, 2nd have 2 friends, 3d have 2 friends, 4fth have 1 friend, so ans is
4
1 2
1 3
1 4
2 3