[shkola] Edna zadachka za wsichki!

Eto wi edna zadachka. Wseki koito q napishe mozhe da kazhe kak q e 
reshil  i da publikuwa source-a si ako zhelae.

Tazi srqda weroqtno nqma da imame shkola. 
Hm, maj shte minem na zadochna forma.
I wse pak ot was zawisi...

Ta eto q zadachkata:

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To help you move from Waterloo to the big city, you are considering 
renting a moving truck. Gas prices being so high these days, you want 
to know how much the gas for such a beast will set you back.

The truck consumes a full litre of gas for each kilometre it travels. It 
has a 200 litre gas tank. When you rent the truck in Waterloo, the tank 
is half full. When you return it in the big city, the tank must be at 
least half full, or you'll get gouged even more for gas by the rental 
company. You would like to spend as little as possible on gas, but you 
don't want to run out along the way.

Input

Input is all integers. The first integer is the distance in kilometres 
from Waterloo to the big city, at most 10000. Next comes a set of up to 
100 gas station specifications, describing all the gas stations along 
your route, in non-decreasing order by distance. Each specification 
consists of the distance in kilometres of the gas station from 
Waterloo, and the price of a litre of gas at the gas station, in tenths 
of a cent, at most 2000.

Output

Output is the minimum amount of money that you can spend on gas to get 
you from Waterloo to the big city. If it is not possible to get from 
Waterloo to the big city subject to the constraints above, print 
"Impossible". 

Sample Input

500
100 999
150 888
200 777
300 999
400 1009
450 1019
500 1399

Output for Sample Input

450550
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-- 
Ivaylo Riskov <ivaylo_riskov@xxxxxxx>

"Do not take life too seriously; you will never get out of it alive."

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