JavaScript program to print sum of n natural numbers

Following program shows you how to print sum of n natural numbers.
In this program we get number from user and shows sum of n natural numbers using following formula
Sum of n natural numbers = input X (input + 1)/2

var input = parseInt(prompt("Enter a number:"));
var result = input * (input + 1) / 2;
console.log(result);

Output:

Enter a number:
4
10