import sys


def solve():
    N, M = map(int, input().split())
    Ds = []
    for i in range(M):
        Ds.append(int(input()))
    Ds.sort()

    ans = float('inf')

    for i in range(M - N + 1):
        ans = min(ans, abs(Ds[i] - Ds[i + N - 1])
                       + min(abs(Ds[i]), abs(Ds[i + N - 1])))

    print(ans)


def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val),
                                    file=sys.stderr)
            return None


if __name__ == '__main__':
    solve()