program fact;
var n,i,j,k:integer;
    p: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;
  n:=p*5;
  u:=true;
  while i<=n do begin
                j:=i;
                k:=0;
                while j<>1 do begin
                              inc(k);
                              j:=j div 5;
                              end;
                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.