#include <fstream.h>
#include <stdlib.h>
#define InFile "nunta.in"
#define OutFile "nunta.out"
int n;
unsigned long long b[1000],x,xx,sol=1;

int main()
{int i,j,q;
ifstream in(InFile);
in>>n;
in.close();
for(i=0;i<n;i++)
{
  b[i]=1;
  x=b[0];
  xx=b[1];

  for(j=1;j<i;j++)
  {b[j]=x+xx;x=xx;xx=b[j+1];}

  if(i>=n-n/2)sol+=b[n-i];
}
ofstream out(OutFile);
out<<sol<<'\n';
out.close();
return 0;
}