Total Distance travelled by a particle?

I need to find the total distance travelled between time t=1 and t=4, which at t=1 velocity of the particle is v=40, at t=4 velocity is 0. (0,0), (40,1), (0,2), (-40,3), (0, 4) = those are the coordinates of the graph. How do I find the total distance? I'm a bit confused because I wasn't given an equation, just a graph