program ciur;
var a:array[1..2000000] of boolean;
   i,j,n,k:integer;
   fi,fo:text;
begin
assign(fi,'ciur.in');reset(fi);
assign(fo,'ciur.out');rewrite(fo);
read(fi,n);
for i:=2 to n do a[i]:=true;
 for i:=2 to n do
       if a[i] then begin 
inc(k);    
for j:=2 to n div i do a[i*j]:=false;
   end;
write(fo,k);
close(fi);close(fo);
end.