#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
using namespace std;
int b[5000000];
int a[5000000];
int n,i,j,k,m=0;
int main()
{
    while(~scanf("%d",&n))
    {
        if(n==-1)
            break;
        memset(a,0,sizeof(a));
        memset(b,0,sizeof(b));
        a[1]=1;
        b[1]=1;
        b[0]=1;
        if(a[n]!=0&&n!=0)
            printf("%d\n",a[n]);
        else
        {
            for(i=1; i<=n; i++)
            {
                m=a[i-1]-i;
                if(m>0)
                {
                    if(b[m]==0)
                    {
                        a[i]=m;
                        b[m]=1;
                    }
                    else
                    {
                        a[i]=a[i-1]+i;
                        b[a[i]]=1;
                    }
                }
                else
                {
                    a[i]=a[i-1]+i;
                    b[a[i]]=1;
                }
            }
            printf("%d\n",a[n]);
        }
    }
    return 0;
}