534. First, camel 1000 radish goes forward x 1 km, puts down 1000-2*x 1 radish, and then takes back the rest x 1 radish; Then camel 1000 radish, take x 1 radish at x 1 km, and let donkey camel 1000 radish; Continue to move forward to the distance of x2 km from the starting point, put down 1000-2*(x2-x 1) radish and return to the starting point after eating radish at x 1 km; Finally, the camel took a thousand radishes and walked to x 1, and x2 took all radishes in turn, and then walked to the end. The remaining radishes at x 1 and x2 are less than or equal to x 1 and (x2-x 1) respectively. Under the constraint of this inequality, it is enough to find the maximum of two remaining radishes, because in fact, the number of two remaining radishes is the number of radishes that can finally reach the end point. Finally, x 1=200, x2= 1600/3. The total distance traveled by donkeys is 2 * x1+2 * x2+1000 = 2466+2/3, which means that only one radish can be eaten after walking one kilometer, that is, the total number of radishes eaten is rounded to 2466, so the radishes that can be sold at last are 3000-2466=534.