We have two numbers a and b that need to be set via the console. And then print the sum of all numbers from a to b. For example a = 13 b = 17. Result: 13+14+15+16+17 = 75 I wonder how this is done

The *idiomatic* Kotlin way to sum all numbers from `a`

to `b`

would be:

```
val sum = (a..b).fold(0) { acc, value -> acc + value }
```

You define a range `[a,b]`

and then sum all numbers up.

To read a number from the `stdin`

you could use the following:

```
val number = readLine()?.toInt()
?: throw IllegalStateException("stdin is not available.")
```

From a performance point of view, it might be better to use this approach:

For the “idiomatic” approach, one could even go with

```
val sum = (a..b).sum()
```