The task is to generate the correct answer for a given math problem.

Ex Input:
Problem: gopi gives rs . 90 plus one turban as salary to his servant for one year . the servant leaves after 9 months and receives rs . 60 and the turban . find the price of the turban .

Ex Output:
30


Ex Input:
Problem: a train running at the speed of 72 km / hr crosses a pole in 9 seconds . find the length of the train .

Ex Output:
180 meter


Ex Input:
Problem: company x provides bottled water to its employees in 10 liter bottles , $ 2 each . at least how many 10 l bottles must company x buy monthly , so that new contract with $ 50 fixed monthly rate and $ 1 for 50 l bottle each paid off ? ( assume that no other costs apply )

Ex Output:

28