1*1/2+1/3*1/4+.+1/2n-1*1/2n
=1/2+1/3-1/4+1/4-1/5+...+1/2n-1-1/2n
=5/6-1/2n>1000/2009
经计算得n>6027/4045>1
所以最小的正整数n=2