When Asking About Longevity, Start with Equivalent Exchange

Qin Fan, a young man with a mole, traveled through time and entered a world of immortality. But as soon as I started, I entered the black mine. What kind of hellish difficulty is this? Fortunately, the "equivalent exchange" system has been awakened. As long as all unused things are exchanged for system spirit stones, even mortals can practice. Only. "Why are they also low-grade spiritual stones? Why can only two and a half spiritual stones be exchanged for one spiritual stone from the system? It's an equal exchange as promised!"