Kill the monster

There is a mountain near yifenfei’s hometown. On the mountain lived a big monster. As a hero in hometown, yifenfei wants to kill it. <br>Now we know yifenfei have n spells, and the monster have m HP, when HP &lt;= 0 meaning monster be killed. Yifenfei’s spells have different effect if used in different time. now tell you each spells’s effects , expressed (A ,M). A show the spell can cost A HP to monster in the common time. M show that when the monster’s HP &lt;= M, using this spell can get double effect.<br>

The input contains multiple test cases.<br>Each test case include, first two integers n, m (2<n<10, 1<m<10^7), express how many spells yifenfei has.<br>Next n line , each line express one spell. (Ai, Mi).(0<Ai,Mi<=m).<br>

For each test case output one integer that how many spells yifenfei should use at least. If yifenfei can not kill the monster output -1.

3 100<br>10 20<br>45 89<br>5  40<br><br>3 100<br>10 20<br>45 90<br>5 40<br><br>3 100<br>10 20<br>45 84<br>5 40<br>

3<br>2<br>-1<br>

yifenfei

奋斗的年代