import sys
input=lambda: sys.stdin.readline().rstrip()
n,m=map(int,input().split())
D=sorted([int(input()) for _ in ragnge(m)])
ans=0
for i in range(m-n+1):
  if D[i]<=0<=D[n-1+i]:
    ans=min(ans,D[n-1+i]-D[i])
  else:
    ans=min(ans,max(D[n-1+i],D[i]))
print(ans)