On 13 June 1990, the East German military officially began dismantling the Wall, beginning in Bernauer Straße and around the Mitte district. From there, demolition continued through Prenzlauer Berg/Gesundbrunnen, Helligensee and throughout the city of Berlin until that December 1990. According to estimates by the border troops, a total of around 1.7 million tonnes of building rubble was produced by the demolition. Unofficially, the demolition of the Bornholmer Straße began because of construction work on the railway. This involved a total of 300 GDR border guards and - after 3 October 1990 - 600 Pioneers of the Bundeswehr. These were equipped with 175 trucks, 65 cranes, 55 excavators and 13 bulldozers. Virtually every road that was severed by the Berlin Wall, every road that once linked from West Berlin to East Berlin, was reconstructed and reopened by 1 August 1990. In Berlin alone, 184 km of wall, 154 km border fence, 144 km signal systems and 87 km barrier ditches were removed. What remained were six sections that were to be preserved as a memorial. Various military units dismantled the Berlin/Brandenberg border wall, completing the job in November 1991. Painted wall segments with artistically valuable motifs were put up for auction in 1990 in Berlin and Monte Carlo.
Question: How many different components (including ditches and signal systems) were removed in Berlin alone?
Answer: 4