2
10
20
1-4
1-3
1-7
1-9
4-5
3+6
7-8
9-10
5+2
6+2
8-2
10+2
7+9
9+3
3+4
4+7
5+8
8+10
10+6
6-5
6
12
1-2
2-3
3-4
4-1
1-5
2-5
3-5
4-5
1-6
2-6
3-6
4-6