var i,n,j,k,l:longint;
    ok:boolean;
    f,g:text;
begin
assign(f,'ciur.in');
reset(f);
assign(g,'ciur.out');
rewrite(g);
readln(f,n);
k:=0;
for i:=2 to n do
    begin
    ok:=true;
       for j:=2 to trunc(sqrt(i)) do
    if i mod j=0 then ok:=false;
    if ok=true then k:=k+1;
    end;
writeln(g,k);
close(f);
close(g);
end.