print((function (f)
	local r = 0
	for _=1,tonumber(io.stdin:read("*l")) do
		r = r + f(io.stdin:read("*l"))
	end
	return r
end)(function (s)
	local t = {}
	s:gsub("%d+", function (e) table.insert(t,tonumber(e)) end)
	local l, r = t[1]*60+t[2], t[3]*60+t[4]
	return l <= r and r-l or 24*60-l+r
end))