PROGRAM POR1;
VAR  N,I,J,s:longint;
      V:ARRAY[1..100]OF BOOLEAN; f,g:text;
BEGIN
      assign(f,'ciur.in');reset(f);
      assign(g,'ciur.out');rewrite(g);READLN(f,N);
      FOR I:=2 TO N DO
       IF not (V[I]) THEN  begin
        inc(s);
          FOR J:=2 TO N DIV I DO
           V[I*J]:=true;
       END;write(g,s); close(f);
       close(g);
END.