how to solve this error

Arduino: 1.8.1 (Windows 8.1), Board: “Arduino/Genuino Uno”

C:\Users\Supun\Downloads\Obstacle_Avoiding\Obstacle_Avoiding.ino:7:56: fatal error: AFMotor.h: No such file or directory

#include <AFMotor.h> //import your motor shield library

^

compilation terminated.

exit status 1
Error compiling for board Arduino/Genuino Uno.

This report would have more information with
“Show verbose output during compilation”
option enabled in File → Preferences.

Where did you put the AFMotor library?
The compiler can't find it.