B = int(input())
N = int(input())
C = [0]*N
sum = 0
cnt = 0

for i in range(N):
    C[i] = int(input())
    sum += C[i]
ave = int((sum+B)/N)
C.sort()
C.reverse()
'''
print(C)
for i in range(N):
    j = 0
    if C[i]>ave:
        for j in range(C[i]-ave):
            C[i] -= 1
            cnt += 1
            B += 1
    elif C[i]<ave and B>0:
        for j in range(ave-C[i]):
            C[i] += 1
            cnt += 1
            B -= 1

print(cnt)
#print(C)
'''
for i in range(N):
    if C[i]>ave:
        cnt += C[i]-ave
    elif C[i]<ave:
        cnt += ave-C[i]        

print(cnt)