B = input()
N = input()
C = [int(raw_input()) for _ in xrange(N)]
avg = sum(C)/N+1

amari = sum(c-avg for c in C if c > avg)
tarinai = sum(avg-c for c in C if c < avg)
ans1 = amari+tarinai if amari+B >= tarinai else float('inf')
avg -= 1
amari = sum(c-avg for c in C if c > avg)
tarinai = sum(avg-c for c in C if c < avg)
ans2 = amari+tarinai

print min(ans1, ans2)