78. Xiao Jie and Xiao Qiao are running along the circular path in the park. Xiao Jie is still $400 \mathrm{~m}$ short of completing 2 laps, and Xiao Qiao is still $500 \mathrm{~m}$ short of completing 3 laps. Together, they have run a total of 4 laps plus $100 \mathrm{~m}$. The length of this circular path is $\qquad$ $\mathrm{m}$.
answer: 1000