program factorial;
var f,g:text;
    p,n,m,s:longint;
begin
assign (f,'fact.in'); reset (f);
assign (g,'fact.out'); rewrite (g);
read (f,p);
if p=0 then write (g,'1')
       else begin n:=p*4;
                  repeat m:=5;
                         s:=0;
                         while m<=n do begin s:=s+(n div m) ;
                                             m:=m*5;
                                       end;
                         inc(n);
                  until (s=p) or (s>p);
                  if s=p then write(g,n-1)
                         else write(g,'-1');
            end;
close (f);
close (g);
end.