(function (f)
	local r=0
	for _=1,io.stdin:read("*n") do r=r+f() end
	print(r)
end)((function (ffi)
	ffi.cdef 'int scanf(const char *, ...);'
	local C,ct = ffi.C,ffi.typeof("int8_t[1]")
	local h = { ct();ct();ct();ct() }
	return function ()
		C.scanf("%d:%d%d:%d",h[1],h[2],h[3],h[4])
		local r = h[3][0]*60+h[4][0] - (h[1][0]*60+h[2][0])
		return r<0 and 24*60+r or r
	end
end)(require'ffi'))