2000-3-6-9-...-51-54
=2000-18*(3+54)/2
=2000-513
=1487
(2+4+6...+98+100)-(1+3+5...+97+99)
=(2-1)+(4-3)+(6-5)+……+(98-97)+(100-99)
=1+1+1+……+1+1
=50
2000-3-6-9-...-51-54
=2000-18*(3+54)/2
=2000-513
=1487
(2+4+6...+98+100)-(1+3+5...+97+99)
=(2-1)+(4-3)+(6-5)+……+(98-97)+(100-99)
=1+1+1+……+1+1
=50