using namespace std;
int main(){
int n;
int a1=2;
int d=3;
while(cin>>n){
int sn=a1*n+n*(n-1)*d/2;
cout<<sn<<endl;
}
}
using namespace std; int main(){ int n; int a1=2; int d=3; while(cin>>n){ " >
using namespace std;
int main(){
int n;
int a1=2;
int d=3;
while(cin>>n){
int sn=a1*n+n*(n-1)*d/2;
cout<<sn<<endl;
}
}