def int_ternary_search(f, lo: int, hi: int) -> int:
    l = lo
    r = hi
    while r - l > 3:
        m1 = l + (r - l) // 3
        m2 = r - (r - l) // 3
        if f(m1) > f(m2):
            l = m1
        else:
            r = m2

    ind = l
    best = f(l)
    for i in range(l, r+1):
        v = f(i)
        if v < best:
            best = v
            ind = i

    return ind


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


lo = min(C)
hi = max(C)
res = int_ternary_search(f, lo, hi)
print(f(res))