Finally I got accepted. I include several tests to help you debug:
input            output:
8                YES
1 70             1 70
4 65             4 65
64 66            61 64
61 64            65 64
66 62            66 64
80 50            66 62
80 60            80 60
65 64            80 50

input:           output:
3                YES
1 3              1 3
2 1              1 2
2 3              3 2