y+999=9999999999
y=999999999-999
y=9999999000
y+999=9999999999
y+999=9999999999
y=999999999-999
y=9999999000
Vậy x=9999999000
y+999=9999999999
y=9999999999-999
y=9999999000
y + 999 = 9999999999
y = 9999999999 - 999
y = 9999999000
Vậy y = 9999999000