|1-({1\over a_0}+{1\over a_1}+...+{1\over a_l}+{1\over a_{l+1}})|=|{1\over {s_{l+1}-1}}-{1\over {a_{l+1}}}|=|{(a_{l+1}-(s_{l+1}-1))\over {(s_{l+1}-1)a_{l+1}}}|