A traffic light at the turn for the “MEGA” shopping center from the
Novomoskovskiy highway works in such a way that k cars are able to
take a turn in one minute. At weekends all the residents of the city
drive to the mall to take a shopping, which results in a huge traffic
jam at the turn. Administration of the mall ordered to install a camera
at the nearby bridge, which is able to calculate the number of cars
approaching this turn from the city. The observation started n minutes ago.
You should use the data from the camera to determine the number of cars
currently standing in the traffic jam.
Input
The first line contains integers k and n (1 ≤ k, n ≤ 100), which
are the number of cars that can take a turn to “MEGA” in one minute
and the number of minutes passed from the beginning of observation.
The second line contains spaceseparated integers a_{1}, …, a_{n}
(0 ≤ a_{i} ≤ 100), where a_{i} is the number of cars that approached the turn
during the ith minute. The observation started at morning, when there
were no cars at the turn.
Output
Output the number of cars currently standing in the traffic jam.
Samples
input  output 

5 3
6 7 2
 0

5 3
20 0 0
 5

Problem Author: Bulat Zaynullin
Problem Source: Ural Regional School Programming Contest 2010