rogram ciurul;
var n,i,j,k:longint;
a : array [1..3000000] of boolean;
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 begin
                if not a[i] then begin
    inc(k);
      for j:=2 to n div i do 
         a[i*j]:=true;
       end;
                  end;
write(fo,k);
close(fo);
end.