1.
A person facing west from point O walks 4 km to reach point A, then from there he walks 4 km to the right and reaches point B, then walks 4 km to the right and reaches point C, turns right and walks 3 km to reach point D, turns left 4 km to reach point E, walks 5 km to the right and arrives at point F, The shortest distance (in km) between point D and point B is: