var f,g:text;
    a:array[1..2000000000]of boolean;
    i,x,n,nr:longint;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n);
for i:=2 to n do a[i]:=true;
for i:=2 to n do
 if a[i]=true then begin
  x:=i+i;
  while x<=n do begin
   a[x]:=false;
   inc(x,i);
  end;
 end;
nr:=0;
for i:=2 to n do
 if a[i]=true then inc(nr);
writeln(g,nr);
close(f);
close(g);
end.