#!/usr/bin/env python3
n, m = map(int,input().split())
d = list(sorted(map(lambda _: int(input()), range(m))))
ans = float('inf')
for l in range(m):
    try:
        r = l + n - 1
        if d[l] < d[r] <= 0:
            acc = - d[l]
        elif 0 <= d[l] < d[r]:
            acc = d[r]
        else:
            acc = max(- d[l], d[r]) + 2 * min(- d[l], d[r])
        ans = min(ans, acc)
    except Exception as e:
        pass
print(ans)