var f,g:text;
    p,n,cifra,nr:longint;
    gasit:boolean;
begin
assign(f,'fact.in'); reset(f);
assign(g,'fact.out'); rewrite(g);
read(f,p);
n:=p*5;
gasit:=false;
nr:=5;
while n div nr>0 do begin
    cifra:=cifra+n div nr;
    nr:=nr*5;
end;
while (gasit=false) and (cifra>=p) do begin
  nr:=5;
  cifra:=0;
  while n div nr>0 do begin
    cifra:=cifra+n div nr;
    nr:=nr*5;
  end;
  if cifra=p then gasit:=true
             else n:=n-(cifra-p)*5;
end;
if gasit=true then write(g,cifra)
              else write(g,'-1');
close(g);
end.