In 1939, aged 12, he enrolled in a minor seminary in Traunstein. This period lasted until the seminary was closed for military use in 1942, and the students were all sent home. Ratzinger returned to the Gymnasium in Traunstein. During this period in the seminary, following his 14th birthday in 1941, Ratzinger was enrolled in the Hitler Youth, as membership was legally required as of 25 March 1939. Following the seminary closure he continued required attendance with the Hitler Youth to avoid financial penalties in the Gymnasium tuition fees. The financial penalty (which theoretically required documentation of attendance at Hitler Youth activities) was overlooked when a sympathetic mathematics professor allowed him not to attend any meetings. In Ratzinger's book "Salt of the Earth", Ratzinger says the following "... Thank goodness, there was a very understanding mathematics teacher. He himself was a Nazi but an honest man, who said to me, 'Just go once and get the document so that we have it' ... When he saw that I simply didn't want to, he said, 'I understand, I'll take care of it', and so I was able to stay free of it."