var v:array[2..2000000] of 0..1;
n,i,j,nr:longint;
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 v[i]=0 then
       begin
       nr:=nr+1;
       j:=i*i;
       repeat
             v[j]:=1;
             j:=j+i;
       until j>n;
       end;
write(g,nr);
close(f);close(g);
end.