No problem, we've got 4099 and 1621 to multiply
4099 × 1621 = 1621 × (4099)
+ 1621 × 9 what gives us 14589
+ 1621 × 90 producing 145890
+ 1621 × 000 that equals 0
+ 1621 × 4000 that is equal 6484000

= 6644479
