Program ciur;
var val : array[1..2000000] of 0..1;
    n,a,b,c,j,aux,sol : longint;
    i : longint;
begin
    assign(input,'ciur.in'); reset(input);
    assign(output,'ciur.out'); rewrite(output);
    readln(n);
    for i:=2 to n do val[i]:=0;
    for i:=2 to n do
        if val[i]=0 then begin
                            sol:=sol+1;
                            aux:=2;
                            j:=i*2;
                            while j<=n do begin
                                              val[j]:=1;
                                              aux:=aux+1;
                                              j:=i*aux;
                                          end;
                            end;
    writeln(sol);

    close(input);
    close(output);
end.