Prabhu travelled in the east direction from his house a distance of 20 km to his friend's house. After some time he left his friend’s house and took a turn towards right and travelled 15 km to reach a park. After resting for a while, he again started and turned to right and travelled 18 km to reach a petrol bunk. From there he again turned right and covered a distance of 15 km. How many km more he has to travel to reach home?