A 'for' loop with ";" at the end

I found the following code:

int func_prim (int zahl) {
  int count;
  if (zahl < 0)
    return -1;

  for (count = 2; zahl % count != 0 && zahl >= count; count++);
  if (count == zahl)
    return 1;
  return 0;
}

The point of function is to check whether a number is a prime number or not.

I don't understand why the for-loop has ; at the end:

                                                            v
for (count = 2; zahl % count != 0 && zahl >= count; count++);

Without that, the code doesn't work properly.

What is the explanation?