The minus-operator is read from right to left, and in your code does one of the minus-operations miss a value on the left side. It's on line six, where you're having to minus-operators in a row:
Either remove one of the minuses, or put something in between. Here is it with one of them removed:
That would work.
Another thing is your coding style. You should try staying to the standards, and don't be using non-compiler-independent libraries like conio.h. Your main-function is also wrong. It shall return an integer, and not
nothing.