Input, PRGM:I/O:1, is a command which will display a string, and will wait for a value to be entered. It will then store that value into the provided variable once ENTER is pressed. If the only argument is a variable, then a question mark will be displayed instead of the string. And if no arguments are provided, then a cursor on the graph screen will be used to define coordinates at a given location to the variables X and Y.