program expresie;
type vector=array[1..2032000] of qword;
     vector1=array[1..2032000] of 0..1;
var  w:vector; ok:boolean; v:vector1;
     i,n,k,j:longword; nr:qword;
     f,g:text;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n); ok:=true; nr:=0;
for i:=2 to n do v[i]:=1;
for i:=2 to n do
 if (v[i]<>0)then begin
                  inc(nr); j:=2*i;
                  while (j<=n)do begin
                                 v[j]:=0; inc(j,i);
                                 end;
                  end;
writeln(g,nr);
close(f);close(g);
end.