Installing after broken installation

Hello everybody! Please help me to solve this problem.

I tried to install iTunes,the installation was not finished because of emergency reboot. Next try of installation: installation wizard refuses to install iTunes explaining that "can`t install it because the copied file already exists".

Of course, dear wizard, it exists - you installed it there 🙂 - I try to expain it to him but he, as you can guess, doesn`t react 😟