program p1;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var n,i,j,p,t:longint;
begin
assign (input,'input.txt');
reset(input);
assign (output,'output.txt');
rewrite(output);
t:=0;
readln(n);
for i:=2 to n do
begin
p:=0;
for j:=2 to round(sqrt(i)) do
if i mod j=0 then p:=1;
if p=0 then t:=t+1;

end;
writeln(t);
close(input);
close(output);



end.