-100-99-98-..-2-1-0+1+2+..+48+49+50

-100 - 99 - ... - 50 - 49 ... - 0 + 1 + ... + 49 + 50
= -100 - 99 - 98 - ... - 51 + 0
= -(100 + 99 + 98 + ... + 51) ---> n = 50
= -((100 + 51) + (99 + 52) + ... + (76 + 75))
= -(151 × 50/2)
= -(151 × 25)
= -3775