program fact;
var k,i:integer;
    p,n:qword;
    u:boolean;
    f,g:text;
begin
  assign(f,'fact.in'); reset(f); readln(f,p);  close(F);
  assign(g,'fact.out'); rewrite(g);
  i:=25;  k:=1;
  n:=p*5;
  u:=true;
  while i<=n do begin
                inc(k);
                n:=n-5*(k-1);
                if n<i then begin
                            u:=false;
                            break;
                            end;
                i:=5*i;
                end;
  if not(u) then write(g,-1)
            else write(g,n);
  close(g);
end.