program factorial;
var p,i,nr:longint;
    rez:real;
    f,g:text;
    cond:boolean;
    aux:int64;
begin
assign (f,'fact.in'); reset (f);
assign (g,'fact.out'); rewrite (g);
read (f,p);
aux:=5;
cond:=false;
nr:=0;
while (aux<5*p) do begin aux:=aux*5;
                         nr:=nr+1;
				   end;			   
aux:=aux div 5;
nr:=nr-1;
if (p<>0) then begin rez:=int(5*(p-nr{int(ln(5*p)/ln(5)-1)}));
                     write (g,rez:10:0);
               end
          else if (p=0) then write (g,'1')
                        else if (cond) then write (g,'-1');
close (f);
close (g);
end.