program fvc;
var f,g:text;
n,numar,nr,c:longint;
bifat:array of integer;
begin
   assign(f,'ciur.in'); reset(f);
   assign(g,'ciur.out'); rewrite(g);
   read(f,n);
   setlength(bifat,n+1);
      numar:=2;
        while numar<=n do
           begin
              if bifat[numar]=0 then
              begin
              c:=c+1;
              nr:=numar;
                 while nr<=n do
                   begin
                      bifat[nr]:=1;
                      nr:=nr+numar;
                   end;
               end;
           numar:=numar+1;
           end;
           write(g,c);
   close(f);
   close(g);
end.