var v:array[1..2000000] of byte;
    n,i,j,k:longint;
    f,g:text;
begin
     assign(f,'ciur.in'); reset(f);
     assign(g,'ciur.out'); rewrite(g);
     readln(f,n);
     v[1]:=1;
     for i:=2 to trunc(sqrt(n)) do
         for j:=2 to n div i do
             v[i*j]:=1;
     if n=2 then k:=1
            else begin i:=3;
                       while i<=n do
                         begin
                         if v[i]=0 then k:=k+1;
                         i:=i+2;
                         end;
                       end;
     write(g,k);
     close(f); close(g);
end.