var n,i,k,j:integer;
    int,out:text;
    o:boolean;
begin
assign(int,'ciur.in');
assign(out,'ciur.out');
reset(int);rewrite(out);
read(int,n);
j:=0;
for i:=2 to n do
    begin
    o:=true;
    for k:=2 to i div 2 do if i mod k = 0 then o:=false;
    if o then j:=j+1;
    end;
write(out,j);
close(int);close(out);
end.ose(int);close(out);
end.