var i,j,n,nr:longint;
    v:array[1..2000001] of 0..1;
begin
assign(input,'ciur.in'); reset(input);
assign(output,'ciur.out'); rewrite(output);
readln(n);
for i:=2 to n do v[i]:=1;nr:=0;
for i:=2 to n do
   if v[i]=1 then
      begin
        inc(nr);
        j:=2*i;
        while (j<=n) do
           begin
             v[j]:=0;
             j:=j+i;
           end;
      end;
writeln(nr);
close(output);
close(input);
end.