A mother was searching for her son in different directions. After walking straight in the East direction for 5 km, she turned right and walked 4 km in the same direction. After that, she realized that he might go to his friend's house so she turned left and walked for 3 km to reach his friend's house but he was not there. She turned right and walked for 4 km and turned right again and walked for 3 km and finally found her son. What is the shortest distance between her final position and his friend's house?