def start():
     var sPrice, minPrice, cost, numShares, tick_z

     tick_z = 0

     while 0<=minPrice and minPrice<sPrice:
         prob(1,3):
            sPrice=sPrice+1
         else:
            sPrice=sPrice-1

         numShares = unif(-2,3)

         while numShares>0:
             numShares=numShares-1
             tick_z=tick_z+sPrice

         while numShares<0:
             numShares=numShares+1
             tick_z=tick_z-sPrice

     tick(tick_z)