#include <bits/stdc++.h>

using namespace std;

long sumOfGroup(int k) {
    // Return the sum of the elements of the k'th group.
    int l=k-1;
    int s=(l*(l+1))/2;
    l=1;
    int c=-1;
    while(1)
    {
        if(s==c)
            break;
       if(l%2==1)
            c++;
        l+=2;
    }
    int sum=0;
    for(int i=0;i<k;i++)
    {
        if(l%2==1)
            sum+=l;
    }
    return sum;
}

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