{2: 1, 20: 1}
15 20
{2: 1, 20: 1, 5: 2, 15: 2}
16 20
{2: 1, 20: 1, 5: 2, 15: 3, 10: 3, 16: 3}
{2: 1, 20: 2, 5: 2, 15: 4, 10: 4, 16: 4, 7: 3}
9 10
{2: 1, 20: 2, 5: 2, 15: 4, 10: 4, 16: 4, 7: 4, 9: 4}
4