INF = 1 << 60
B = int(input())
N = int(input())
C = [int(input()) for _ in range(N)]
C.sort(reverse=True)


def f(v: int) -> int:
    t = B
    res = 0
    for c in C:
        if c > v:  # 多い
            t += c - v
            res += c - v
        elif c < v: # 少ない
            if v - c > t: return INF
            t -= v - c
            res += v - c

    return res


res = f(C[N // 2])
#if N % 2 == 0:
#    res = min(res, f(C[N // 2 - 1]))
print(res)