var f,g:text; p,n,m,s:longint;
begin
  assign(f, 'fact.in');
  assign(g, 'fact.out');
  reset(f);
  rewrite(g);
  readln(f,p);
  n:=0; m:=1; s:=1;
  for i:=1 to p do
  s:=s*10;
 while m mod s<>0 do
 begin
 inc(n);
 m:=m*n;
 end;
  write(g, n);
  close(f); close(g);

end.