Calculate: 100+99-98-97+96+95-94-93+\cdots +4+3-2-1=
100+99-98-97+96+95-94-93+\cdots +4+3-2-1
=(100+99-98-97)+(96+95-94-93)+\cdots +(4+3-2-1)
=4\times25
=100