program ciur;
var x,i,n,nr:longint;
    cond:boolean;
    f,g:text;
begin
assign (f,'ciur.in'); reset (f);
assign (g,'ciur.out'); rewrite (g);
x:=2;
nr:=0;
read (f,n);
while (x<=n) do begin cond:=true;
                      for i:=2 to x div 2 do if (x mod i=0) then cond:=false;
                      if (cond=true) then nr:=nr+1;
                      x:=x+1;
                end;
writeln (g,nr);
close (f);
close (g);
end.