[백준] 8393번 : 합 - Javascript(자바스크립트)

https://www.acmicpc.net/problem/8393

const fs=require('fs')
let input=fs.readFileSync('/dev/stdin').toString()
var n=parseInt(input)
var sum=0
if(n%2==1){
    var m=parseInt((n+1)/2)
    sum=(1+n)*parseInt(n/2)+m
} 
else sum=(1+n)*parseInt((n+1)/2)
console.log(sum)