（224+1/222）x1/223
=(223+1+1/222)x1/223
=(223+223/222)x1/223
=1+1/222
=223/222;

1/128+1/64+1/32+...+1/4
=1/128+2/128+4/128+8/128+16/128+32/128
=(1+2+4+8+16+32)/128
=63/128