object Solution {
    
    def sumUntilN(n:Long):Long = {
        val result:Long = n*(n+1)/2
        return(result)
    }

    def sumOfGroup(k: Int): Long =  {
        var groupRefStart = sumUntilN((k-1).asInstanceOf[Long])
        var result:Long = 2*(sumUntilN(groupRefStart+k) - sumUntilN(groupRefStart))-k
        return(result)
    }

    def main(args: Array[String]) {
        val sc = new java.util.Scanner (System.in);
        var k = sc.nextInt();
        val answer = sumOfGroup(k);
        println(answer)
    }
}