Program cmmdc2;
var p,n,v,c: longint;
    f1,f2:text;

Begin
     assign(f1, 'fact.in' );
     assign(f2, 'fact.out');
     reset(f1);
     readln(f1,p);
     close(f1);
     if p=0 then n:=1 else
     Begin
          n:=p*5;
          v:=25;
          while v<=n do
                Begin
                     c:=v;
                     while c<=n do
                           Begin
                                n:=n-5;
                                if n<c then n:=-1;
                                c:=c+v;
                           end;
                     v:=v*5;
                end;
     end;
     rewrite(f2);
     writeln(f2,n);
     close(f2);
end.