a duck hunter favorite thing hunt he live dimensional world locate point 00 as do not like walk prey prefer shoot vertically case duck fall straight hand the hunter do not reload gun immediately r second pass shot when hunter shoot bullet immediately hit duck directly hunterin dimensional world duck horizontal segment move horizontally negative direction Ox axis speed 1 length unit second for duck know value hi ti xcoordinate head leave end segment tail right end segment time 0 the height duck flying is not important gun shoot vertically infinite height hit duck way the figure sample what maximum number duck hunter shoot the duck consider shot hunter moment shot point intersect Oy axis after hunter shoot duck fall can not shot anymore the hunter shot moment time 0