So you start with a value for `num`

- say 10.

Fibonacci sequence adds the previous two numbers in the sequence together - 0 + 1 is 1, 1 + 1 is 2, 1 + 2 is 3, 2 + 3 is 5 and so on.

So the `fib`

array starts at [1, 1]: itβs always an array with at least two elements, and those two elements have to be the start of the sequence (can be 0 and 1, makes no difference to the end result).

The loop starts with a counter `i`

at 0. Itβs going to stop when `num - fib[i + 1]`

is > `fib[i]`

: ie when the target number minus the last element in the array is greater than the second-last element in the array.

The aim of the loop is to add a value to `fib`

on each iteration, and itβs going to move through the the array and look at the value behind that.

So `num`

is 10, `fib`

is `[1,1]`

, `i`

is `0`

```
fib[i] <= num - fib[i + 1]
1 <= 10 - 1
true
// so
fib.push(fib[i] + fib[i + 1])
fib.push(1 + 1)
fib.push(2)
```

So `num`

is 10, `fib`

is `[1,1,2]`

, `i`

is `1`

```
fib[i] <= num - fib[i + 1]
1 <= 10 - 2
true
// so
fib.push(fib[i] + fib[i + 1])
fib.push(1 + 2)
fib.push(3)
```

So `num`

is 10, `fib`

is `[1,1,2,3]`

, `i`

is `2`

```
fib[i] <= num - fib[i + 1]
2 <= 10 - 3
true
// so
fib.push(fib[i] + fib[i + 1])
fib.push(2 + 3)
fib.push(5)
```

So `num`

is 10, `fib`

is `[1,1,2,3,5]`

, `i`

is `3`

```
fib[i] <= num - fib[i + 1]
3 <= 10 - 5
true
// so
fib.push(fib[i] + fib[i + 1])
fib.push(3 + 5)
fib.push(8)
```

So `num`

is 10, `fib`

is `[1,1,2,3,5,8]`

, `i`

is `4`

```
fib[i] <= num - fib[i + 1]
5 <= 10 - 8
false
// loop ends
```

`fib`

is now `[1,1,2,3,5,8]`

. Filter that for odd numbers, then sum.