program factorial;
var p,i,j,k:longint;
st:boolean;
f,g:text;
begin
  assign(f,'fact.in'); assign(g,'fact.out');
  reset(f); rewrite(g);
  read(f,p);
  if p=0 then writeln(g,'1')
  else
  begin
    st:=false;
    k:=0;
    i:=0;
    while not st do
    begin
      k:=k+5;
      j:=k;
      while j mod 5=0 do
      begin
        j:=j div 5;
        i:=i+1;
      end;
    if i=p then begin writeln(g,i); st:=true; end;
    if i>p then begin writeln(g,'-1'); st:=true; end;
    end;
  end;
  close(f); close(g);
end.