Problems

# Minibuses

At the rush hour, three minibuses arrived to the station at the same time, following the same route, into which the passengers immediately got crowded. The drivers found that the number of people in different minibuses is different, and they decided to reallocate a part of passengers so that in each minibus there was an equal number of passengers. Determine the minimum number of passengers to reallocate.

#### Input

Three positive integers, not greater than 100 - the number of passengers in the first, second and third minibus.

#### Output

Print the minimum number of passengers to reallocate. If this is not possible, print the word "IMPOSSIBLE".

Time limit 1 second
Memory limit 122.17 MiB
Input example #1
1 2 3

Output example #1
1

Input example #2
99 100 100

Output example #2
IMPOSSIBLE