p cnf 20 45
-1 -5 0
-1 -9 0
-1 -13 0
-1 -17 0
-5 -9 0
-5 -13 0
-5 -17 0
-9 -13 0
-9 -17 0
-13 -17 0
-2 -6 0
-2 -10 0
-2 -14 0
-2 -18 0
-6 -10 0
-6 -14 0
-6 -18 0
-10 -14 0
-10 -18 0
-14 -18 0
-3 -7 0
-3 -11 0
-3 -15 0
-3 -19 0
-7 -11 0
-7 -15 0
-7 -19 0
-11 -15 0
-11 -19 0
-15 -19 0
-4 -8 0
-4 -12 0
-4 -16 0
-4 -20 0
-8 -12 0
-8 -16 0
-8 -20 0
-12 -16 0
-12 -20 0
-16 -20 0
4 3 2 1 0
8 7 6 5 0
12 11 10 9 0
16 15 14 13 0
20 19 18 17 0