#!/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 - n + 1):
    r = l + n - 1
    if d[l] <= d[r] <= 0:
        acc = - d[l]
    elif 0 <= d[l] <= d[r]:
        acc = d[r]
    else:
        assert d[l] <= 0 <= d[r]
        acc = max(- d[l], d[r]) + 2 * min(- d[l], d[r])
    ans = min(ans, acc)
print(ans)