print((function (f, g, _, s)
	return f(g(s))
end)(function (a)
	local r = #a>1 and a[2]-a[1] or 0
	for i=2,#a-1 do if a[i+1]-a[i]<r then r=a[i+1]-a[i] end end
	return r
end, function (s)
	local h,a = {},{}
	for e in s:gmatch("%d+") do h[tonumber(e)]=0 end
	for k,_ in pairs(h) do table.insert(a,k) end
	table.sort(a)
	return a
end, io.stdin:read("*l"), io.stdin:read("*l")))