#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int k) 
{
    int m,c=0,sum=0,i;
    m=1;
    for(i=1; ; i=i+2)
    {
        if(m==(k))
        {
            //cout<<i<<" ";
            sum=sum+i;
        }
        c++;
        if(c==m)
        {
            m++;
            c=0;
            if(m==(k+1))
                break;
        }
    }
    return sum;
}

int main() {
    int k;
    cin >> k;
    long answer = sumOfGroup(k);
    cout << answer << endl;
    return 0;
}