In the country of four,there are four cities a,b,c,d.b is to the east of a,c is the south of b,d is to the west of c,& a is the north of d.the government wants to connect four cities by road such that person can go to other four cities also.at the same time minimum length of road.a to b,b to c,c to d,d to a,are equal to 10 know.what should be the minimum length of the road?