{3: 1, 9: 1}
{3: 1, 9: 2, 7: 2, 20: 1}
{3: 1, 9: 2, 7: 2, 20: 2, 15: 3}
19 20
{3: 2, 9: 3, 7: 3, 20: 2, 15: 4, 19: 4}
5 7
{3: 3, 9: 3, 7: 3, 20: 2, 15: 4, 19: 4, 1: 3, 5: 3}
4