Dear reader,
Please help me find the name of the film described below:

This is about 20-30 y/o french film about a poor medical school student, who bets with a wealthy millionaire that he can voluntarily be confined in a room without any outside contact for one full year, for one million franks. All he asks for is an access to books.
The millionaire leaves the door of the room open, and spreads flour on the floor to make sure the student has not come out and in. Within that year the millionaire's business suffers big losses, and he decides to kill the student and hide the body, and tell evetryone the student has left. When, the last night he enters the room, he grabs a pillow thinking of sufficating the student. Right before he is about to do that, he notices a letter on the student's desk addressed to the millionaire, in which the student states that as he was so enlightened by reading so many books, the money has lost its value/meaning for him, and he will be leaving very early in the morning, without collecting the bet money.