print((function (f, g, fh)
	local a,h,r = {},{},10e5+1
	for _=1,fh() do f(a,h,fh()) end
	table.sort(a)
	for i=1,#a-1 do r=g(a,i,r) end
	return r~=10e5+1 and r or 0
end)(function (a, h, n)
	if h[n]==nil then a[#a+1],h[n]=n,true end
end, function (a, i, n)
	return a[i+1]-a[i]<n and a[i+1]-a[i] or n
end, (function (M)
	M.cdef 'int scanf(const char *, ...);'
	local C,c = M.C,M.new("int[1]")
	return function () C.scanf("%d",c) return c[0] end
end)(require'ffi')))