0
{2: 1, 18: 1}
{2: 2, 18: 2, 1: 1, 19: 1}
{2: 2, 18: 2, 1: 1, 19: 1, 7: 1, 8: 1}
{2: 2, 18: 2, 1: 1, 19: 1, 7: 1, 8: 1, 3: 1, 5: 1}
{2: 2, 18: 3, 1: 1, 19: 2, 7: 1, 8: 1, 3: 1, 5: 1, 17: 1, 20: 1}
3