How many men survived the selection in Night by Elie Wiesel?

Elie and his father endure several "selections" during the course of their ordeal in Nazi concentration camps during World War I. A selection made the difference between life and death. In the initial selection at Birkenau they are advised to lie about their ages in order to avoid being pointed to the right (sometimes the left was death and sometimes the right) and certain death by the infamous Dr. Mengele, who presided over many of the selections in the camps affiliated with Auschwitz. Later, before they board a train to Buchenwald, the weak, those who would be killed, were pointed to the left and the stronger men to the right. During this selection, when he sees his father has been marked for death, Elie risks his life to bring him back to the right. Unfortunately, Elie's father dies at Buchenwald. How many survived the various selections is unclear. At the end of the war the total number of Jews killed was estimated at over six million, and some think the number much higher. One thing for sure is that when American troops liberated Buchenwald in the spring of 1945 there were 20,000 prisoners still alive, among them Elie Wiesel. These prisoners would have all survived at least one selection, and for most many more.
https://encyclopedia.ushmm.org/content/en/article/liberation-of-nazi-camps