import java.io.*;

class Main{

static final PrintWriter out=new PrintWriter(System.out);

public static void main(String[] args) throws IOException{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String line="";
while((line=br.readLine())!=null&&!line.isEmpty()){
long n=Long.parseLong(line);
long k=(long)n/2;
long ans=-k*k+n*k+n;
out.println(ans);
out.flush();
}
}
}