Excerpt from Free as in Freedom:
Like Math 55, the Putnam was a brutal test of merit. A six-hour exam in two parts, it seemed explicitly designed to separate the wheat from the chaff. Breidbart, a veteran of both the Science Honors Program and Math 55, describes it as easily the most difficult test he ever took. "Just to give you an idea of how difficult it was," says Breidbart, "the top score was a 120, and my score the first year was in the 30s. That
score was still good enough to place me 101st in the country."
Trivia: Richard P. Feynman is a Putnam Fellow.