We navigate to the home directory by running the following command,
$ cd ~
We run the /challenge/run program by giving it's absolute path and give the parameter as ~/w which satisfies the conditions specified. This is required because we are writing the flag to any new file w with it's relative path being equal to three characters.
$ /challenge/run ~/w
We get the flag pwn.college{cEo2md7qzahSd2BdYx94jaPcQop.dNzM4QDL3kTO0czW}