#include<fstream>
using namespace std;
ifstream fin("fractii.in");
ofstream fout("fractii.out");
int v[9999999999],n,i,j,f;
void citire()
	{ int c=1;
	  fin>>n;
		for(i=0;i<n;i++)
		{
		 v[i]=c;
	     c++;
		}
	}
void ir_()
	{ for(i=0;i<n;i++)
		{ for(j=0;j<n;j++)
			{
			  if(v[i]>1&&v[j]>1)
			  {
				  if(v[i]==v[j]+1||v[j]==v[i]+1)
				  { 
				   f++;
				
			      }
			  }
			 if(v[i]==1||v[j]==1)
				 { 
				  f++;
				 
				 }
			}
		}
	
	}
	

int main()
	{ citire();
	 ir_();
	fout<<f;
	 return 0;
	 
	}