def f(x):
    if B + sum(C) >= x * N:
        return sum(abs(C_i - x) for C_i in C)
    else:
        return 10 ** 18

def ternary_search():
    left, right = min(C), max(C)
    
    while right - left > 0.01:
        mid_left = (2*left + right) / 3
        mid_right = (left + 2*right) / 3
        
        if f(mid_left) >= f(mid_right):
            left = mid_left
        else:
            right = mid_right
    
    return f(left)

B = int(input())
N = int(input())
C = [int(input()) for _ in range(N)]
ans = ternary_search()
print(round(ans))