The compound gear train shown in the figure below consists of compound gears B$-$C and D$-$E$.$ All gears are mounted on parallel shafts. The motor shaft rotating at $1000rpm$ is connected to gear $A,$ and the output shaft is connected to gear $F.$ The number of teeth on gear A$,$B$,$C$,$D$,$E and F are $30,50,20,60,20$ and $40,$ respectively. What is the cneed of oear $F?$