import numpy as np


def main():
    b = int(input())
    n = int(input())
    c = np.array([int(input()) for _ in range(n)])
    x = int(np.median(c))  # 中央値

    while x * n > sum(c) + b:
        x -= 1
    ans = sum([abs(i - x) for i in c])
    print(ans)


if __name__ == "__main__":
    main()