#include<bits/stdc++.h>
#define lf double
#define ll long long
#define ull unsigned ll
#define ii pair<int,int>
#define il pair<int,ll>
#define iii pair<ii,int>
#define iiii pair<ii,ii>
#define pll pair<ll,ll>
#define ld long int
#define heap priority_queue
#define mp make_pair
#define st first
#define nd second
#define pb push_back
#define pp pop_back
#define all(x) x.begin(),x.end()
#define len(x) strlen(x)
#define sz(x) (int) x.size()
#define orta ((bas+son)/2)
#define min3(x,y,z) min(min(x,y),z)
#define max3(x,y,z) max(max(x,y),z)
#define dbgs(x) cerr<<(#x)<<" --> "<<(x)<<" "
#define dbg(x) cerr<<(#x)<<" --> "<<(x)<<endl;getchar()
#define MOD 1000000007
#define inf 2000000009
#define N 1005
#define LOG 21
#define K 1005
#define M 105
#define EPS 0.0000001
using namespace std; 

int k;
ull ans;

int main() {

   scanf("%d",&k);

   ll sum=1ll*k*(k-1)/2;

   ll now=sum*2+1;

   for(ll i=now;now+2*k>i;i+=2) ans=ans+i;

   printf("%llu",ans);

}