var v:array[1..2000000]of boolean;n,i,j,s:longint;fi,fo:text;
begin
        assign(fi,'ciur.in');reset(fi);
        readln(fi,n);
        close(fi);
        s:=0;
        for i:=2 to n do
                v[i]:=1;
        for i:=2 to n do
                if v[i]<>0 then begin
                        s:=s+1;
                        j:=i;
                        while j<n do begin
                                j:=j+i;
                                v[j]:=0;
                                end;
                        end;
        assign(fo,'ciur.out');rewrite(fo);
        writeln(fo,s);
        close(fo);
end.