const fi='ciur.in';
      fo='ciur.out';
      nm=2000010;
var p:array[0..nm] of byte;
    n:longint;
    i,j,sol:longint;

procedure ciur;
begin
for i:=2 to n do begin
if p[i]=0 then begin
inc(sol);
j:=i;
   while j<=n do begin
   p[j]:=1;inc(j,i);end;
   end;
 end;
end;

begin
assign(input,fi);reset(input);
readln(n);close(output);
sol:=0;
assign(output,fo);rewrite(output);
ciur;
write(sol);
close(output);
end.