question: What is the nickname of the group that screened out many potential recruits?
context: Following the end of the Second World War, the East German side of the border was guarded initially by the Border Troops (Pogranichnyie Voiska) of the Soviet NKVD (later the KGB). They were supplemented from 1946 by a locally recruited paramilitary force, the German Border Police (Deutsche Grenzpolizei or DGP), before the Soviets handed over full control of the border to the East Germans in 1955/56. In 1961, the DGP was converted into a military force within the National People's Army (Nationale Volksarmee, NVA). The newly renamed Border Troops of the GDR (Grenztruppen der DDR, commonly nicknamed the Grenzer) came under the NVA's Border Command or Grenzkommando. They were responsible for securing and defending the borders with West Germany, Czechoslovakia, Poland, the Baltic Sea and West Berlin. At their peak, the Grenztruppen had up to 50,000 personnel.Around half of the Grenztruppen were conscripts, a lower proportion than in other branches of the East German armed forces. Many potential recruits were screened out as potentially unreliable; for instance, actively religious individuals or those with close relatives in West Germany. They were all subjected to close scrutiny to assure their political reliability and were given intensive ideological indoctrination.A special unit of the Stasi secret police worked covertly within the Grenztruppen, posing as regular border guards, between 1968 and 1985, to weed out potential defectors. One in ten officers and one in thirty enlisted men were said to have been recruited by the Stasi as informers. The Stasi regularly interviewed and maintained files on every guard. Stasi operatives were directly responsible for some aspects of security; passport control stations at crossings were manned by Stasi officers wearing Grenztruppen uniforms.The Grenztruppen were closely watched to ensure that they could not take advantage of their inside knowledge to escape across the border. Patrols, watchtowers and observation posts were always manned by two or three guards at a time. They were not allowed to go out of each other's sight in any circumstances. If a guard attempted to escape, his colleagues were under instructions to shoot him without hesitation or prior warning; 2,500 did escape to the West, 5,500 more were caught and imprisoned for up to five years, and a number were shot and killed or injured in the attempt.
  The work of the guards involved carrying out repair work on the defences, monitoring the zone from watchtowers and bunkers and patrolling the line several times a day. Border Reconnaissance (Grenzaufklärungszug or GAK) soldiers, an elite reconnaissance force, carried out patrols and intelligence-gathering on the western side of the fence. Western visitors to the border were routinely photographed by the GAKs, who also oversaw work detachments maintaining the fence. The workers would be covered by machine guns to discourage them from attempting to escape.
answers.text: Grenzer