
from bisect import bisect_left
n, m = map(int, input().split())
if n in [1, m]:
print(0)
exit()
g = list(map(int, input().split()))
dist = sorted([abs(g[1] - g[0])] +
[max(abs(g[i] - g[i-1]), abs(g[i] - g[i+1])) for i in range(1, n-1)] +
[abs(g[n-2] - g[n-1])])
print(dist[n-m-1])
