I have this code written for a [Project Euler](https://projecteuler.net) problem in c++:

```
int sum = 0;

for(int i =0; i < 1000; i++)
{
    //Check if multiple of 3 but not multiple of 5 to prevent duplicate
    sum += i % 3 == 0 && i % 5 != 0 ? i: 0;
    //check for all multiple of 5, including those of 3
    sum += i % 5 == 0 ? i: 0;
}
    cout << sum;

```

I'm trying to learn `f#` and rewriting this in `f#`. This is what I have so far:

```
open System

//function to calculate the multiples
let multiple3v5 num =
    num

//function to calculate sum of list items
let rec SumList xs =
    match xs with
    | []    -> 0
    | y::ys -> y + SumList ys

let sum = Array.map multiple3v5 [|1 .. 1000|]

```

What I have may be complete nonsense...so help please?