It is a supply problem more than a road problem. Each day won seems small, but it forces you to pay in advance for increasingly expensive logistics.
The messenger and the provisions
Riddle statement
Between a messenger's house and his destination there are seven days of travel. At the end of each day there is a house where he can sleep and leave provisions.
The messenger can only carry food for four days.
He must reach the destination and return home without ever running out of food.
What is the minimum number of days of march he needs in total?