Simple answer, there is no need for you to overflow the buffer here in order to gain access. Since all this program does is compare your input to a fixed string, just provide that value. You are over complicating this question, there is no need to overwrite the existing variable as well in case it was initialized with some value and was being compared with some other value and you had no control over the input, but this is straight forward, even if you have a buffer overflow, what would you use it for, there is no function you want to call or variable you want to overwrite. In case you want to learn when to exploit the buffer overflow and what to do if you have a buffer overflow, checkout this github repo https://github.com/Jeetu855/Binary-Exploitation