package com.company;

import java.util.HashMap;
import java.util.Map;
import java.util.Random;

public class prog {
    public static void main(final String[] args) {
        int sum=15;
        java.util.Scanner scan = new java.util.Scanner(System.in);
        try {
            int n = Integer.parseInt(scan.next());
            if(n>0 && n<=Math.pow(10,6)){

                int sign;
                for(int i=1;i<=n;i++){
                    sign= new Random().nextInt(2);
                    if(sum<=15 || sum-i<15){
                        sum+=i;
                        continue;
                    }
                    if(sign==0){
                        sum+=i;
                    }
                    else{
                        sum-=i;
                    }
                }}
            System.out.println(sum);
        }
        catch (NumberFormatException e){
            System.out.print(15);
            return;
        }


    }
}