One day when you go to a cafe, you see a man in an expensive and neat suit sitting in the corner of the cafe, he looks at you sharply occasionally while opening his cell phone.

After returning from the cafe you lie down on your bed and open your phone, when you open your phone, you see an account following your instagram account.

But what makes you surprised is, it's the man who sat in the corner of the cafe earlier, but how did he know your account?