From Wikipedia’s “Napoleon I of France” (5 July 2006):
The French suffered greatly in the course of a ruinous retreat; the Army had begun as over 650,000 frontline troops, but in the end fewer than 40,000 crossed the Berezina River (November 1812) to escape. In total French losses in the campaign were 570,000 against about 400,000 Russian casualties and several hundred thousand civilian deaths.