# Convert from int to double and back in Cython

This is a really basic question, I'm sure, for cython types.

In the notebook, I have the following cell to compute a famous but totally inefficient $\pi(x)$ (prime counting function). It already is about 100 times faster than the equivalent in native Python.

Question: The `result += (fact - j*int(floor(t)))`

line still is bright yellow. I don't know if there is any easy way to mix these types. The problem is I need for `t`

to take two ints and make them something I can apply floor to, which appears to be a double. Then I need to make the floor an int again to multiply it by `j`

. Any ideas? Again, I'm sure this is simple, but I haven't earned my Cython stripes yet.

```
%cython
cdef extern from "math.h":
double floor(double x)
cdef int primeish(int n):
cdef int fact
cdef int result
cdef int j
cdef double t
if n==1:
return 0
elif n==2:
return 1
elif n==3:
return 2
else:
result = -1
fact = 1
for j in range(3,n+1):
fact = fact*(j-2)
t = fact/j
result += (fact - j*int(floor(t)))
return result
```