Find the atomic mass unit of Sulfur-32 with a mass of 31.972 and percent abundance 94.99%, Sulfur-33 with a mass of 32.971 and percent abundance 0.75%, Sulfur-34 with a mass of 33.968 and percent abundance 4.25%, and Sulfur-36 with a mass of 35.967 and percent abundance 0.01%.