var n,a,b,c,d,e,f,k,nr:0..2000000;
    fin,fout:text;
begin
assign(fin,'fractii.in'); reset(fin);
assign(fout,'fractii.out'); rewrite(fout);
nr:=0;
a:=0; b:=1; c:=1; d:=n;
nr:=n div 2-1;
a:=1; b:=n-nr; c:=1; d:=n-nr-1;
while c<n do
      begin
      inc(nr);
      k:=(n+b) div d;
      e:=k*c-a; f:=k*d-b;
      a:=c; b:=d; c:=e; d:=f;
      end;
nr:=nr*2+1;
writeln(fout,nr);
close(fin); close(fout);
end.