type tablou=array [1..2000000]of 0..1;
var t:tablou;
    i,j,k,n:integer;
    f,g:text;
    begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
rewrite(g);
read(f,n);
for i:=2 to n do
 if t[i]=0 then begin
              inc(k);
             for j:=2 to  n div i do
              t[i*j]:=1;
              end;
write(g,k);
close(f);
close(g);
end.