Why is "$$" the only thing read into my input?

I am trying to have my program read input and whenever "$$" is read the program will terminate and not include $$ however when the program terminates the input is only $$. Previously I was using just cin but I heard that getline will allow me to receive multiple input however this doesn't seem to be the case.

   while (input != "$$") {
        cout << "Enter input: ";
        getline(cin,input);
    }

    cout << input;