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