Kotlin Program:

Example:

import java.util.Scanner
fun main(args: Array<String>) {
  
  print("Enter last number :")
  val userInput = Scanner(System.`in`)
  var n:Int = userInput.nextInt()
  
  print("Sum of 1 to $n : "+ (n*(n+1))/2)
}

Output:

  Enter last number : 10
  Sum of 1 to 10 : 55

We are using the formula of sum of natural numbers (1 to N)

(N*(N+1))/2  // N is the last number