var f:text;i,j,n,s:longint;
    a:array[0..20]of longint;
begin
 assign(f,'text.in');reset(f);read(f,n);close(f);
 a[1]:=5;a[2]:=25;a[3]:=125;a[4]:=625;a[5]:=3125;a[6]:=15625;a[7]:=78125;
 a[8]:=390625;a[9]:=1953125;a[10]:=9765625;
 while(s<n)do
  begin inc(i);
   if i mod a[j+1]=0 then inc(j);
   inc(s,j);
  end;
 if n=0 then i:=1;
 assign(f,'text.out');rewrite(f);if s=n then write(f,i) else write(f,'-1');close(f);
end.