str_N, str_M = input().split(" ")
N = int(str_N)
M = int(str_M)
Ds = []
for i in range(M):
    Ds.append(int(input()))
    
Ds.sort()

ans = []

for i in range(M-N):
    max_value = max(Ds[i:i+N])
    min_value = min(Ds[i:i+N])
    if max_value >= 0 and min_value >= 0:
        ans.append(max_value)
        continue
    if max_value >= 0 and min_value < 0:
        ans.append(min(max_value * 2 + -1 * min_value, max_value + -1 * min_value * 2))
        continue
    if max_value < 0 and min_value < 0:
        ans.append(-1 * min_value)
        
print(min(ans))