var a:array[2..2000000] of boolean;
    i,j,n,k:longint;
    f,g:text;
begin
assign(f,'ciur.in'); reset(f);
assign(g,'ciur.out'); rewrite(g);
readln(f,n); close(f);
fillchar(a,sizeof(a),true);
k:=0;
for i := 2 to trunc(sqrt(n)) do
           if a[i] then begin
                   j:=2;
                   while i*j <=n do begin
                           a[i*j]:=false;
                           inc(j);
                                    end;
                        end;
for i := 2 to n do
      if a[i] then inc(k);
writeln(g,k);

close(g);

end.