program infoarena_factorial;
uses math;
 var p,n:int64;
   f:text;
   function put5(k:int64):int64;
   var p:int64;
   begin       p:=0;
     while k mod 5=0 do
     begin
       p:=p+1;
       k:=k div 5;
     end; put5:=p;
   end;

begin

  assign(f,'fact.in');reset(f);readln(f,p);close(f);
  assign(f,'fact.out');rewrite(f);
 {  write('p=');
  readln(p);        }
  if p=0 then begin n:=1;write(f,n);close(f);end
  else begin
  n:=0;
  while p>0 do
begin
  n:=n+5;
  p:=p-put5(n);
end;
end;
  if p<0 then n:=-1;
  write(f,n);close(f);   {write(n);readln;  }

end.