0
{2: 1, 20: 1}
{2: 1, 20: 1, 5: 1, 15: 1}
{2: 1, 20: 1, 5: 1, 15: 2, 10: 1, 16: 1}
{2: 1, 20: 1, 5: 1, 15: 3, 10: 2, 16: 2, 7: 1}
{2: 1, 20: 1, 5: 1, 15: 3, 10: 2, 16: 2, 7: 1, 9: 1}
3