#include <iostream>
using namespace std;
int main(){
    int k,zbir,i,suma;
    cin>>k;
    zbir=1;
    i=0;
    suma=0;
    while(k>=1){
        suma+=zbir;
        zbir+=3;
        k--;
    
    }
    cout<<suma<<endl;
    


    return 0;
}