46.
The majority of troops who landed on the D-Day beaches were from Great Britain, Canada and the US. However, troops from many other countries participated in D-Day and the Battle of Normandy, in all the different armed services: Australia, Belgium, Czechoslovakia, France, Greece, the Netherlands, New Zealand, Norway and Poland.

Although ultimately successful, the Normandy landings were extremely costly in terms of men and material. The failure of the 3rd Division to take Caen, an overly ambitious target, on the first day was to have serious repercussions on the conduct of the war for well over a month, seriously delaying any forward progress. The fortuitous capture of Villers-Bocage followed by the failure to reinforce it, and its subsequent recapture by the Germans, was again to hamper any attempt to extend the Caen bridgehead and push on. By D+11, June 17th, the assault had stagnated.

A lot of the problem came down to the nature of the terrain in which much of the post-landing fighting took place, the bocages. These were essentially small fields separated by high earth banks covered in dense shrubbery, which were eminently defensible.

In the end the invasion of Normandy succeeded in its objective by sheer force of numbers. Many more troops and equipment continued to come ashore after D-Day. By the end of July, some 1 million Allied troops, mostly American, British and Canadian, were entrenched in Normandy.

More sources:
Decision in Normandy, Carlo D'Este, London, 1983.
The Second World War, John Keegan, Hutchinson, 1989.
Six Armies in Normandy, John Keegan, Penguin, 1994