0
{8: 1, 18: 1}
{8: 2, 18: 1, 1: 1, 11: 1}
{8: 2, 18: 2, 1: 1, 11: 1, 17: 1, 20: 1}
{8: 2, 18: 2, 1: 1, 11: 1, 17: 1, 20: 1, 5: 1}
{8: 2, 18: 1, 1: 1, 11: 2, 17: 2, 20: 1, 5: 1, 9: 1}
2