9999 × 9999 × 9999.

9999 × 9999 × 9999.

9999 × 9999 × 1999, = (10000 - 1) × (10000 - 1) × (2000 - 1), = (10000000 - 2000 + 1) × (200000 - 1), = 20000000 - 40000000 + 2000 - 10000000 + 2000 - 1, = 20000000 - 5000000 + 40000 - 1, = 199500039999.