diff --git a/a8/lisp.cc b/a8/lisp.cc
index e306d41..441e15e 100644
--- a/a8/lisp.cc
+++ b/a8/lisp.cc
@@ -143,9 +143,17 @@ namespace a8
                  [] (const List& params) -> std::shared_ptr<Value>
                  {
                      double result = 0;
-                     for (auto param : *params) {
-                         Atom&& atom = std::any_cast<Atom>(param->value);
-                         result /= atom.val;
+                     if (params->size() > 0) {
+                         result = std::any_cast<Atom>(params->at(0)->value).val;
+                         if (params->size() > 1) {
+                             for (int i = 1; i < params->size(); ++i) {
+                                 auto& param = params->at(i);
+                                 Atom&& atom = std::any_cast<Atom>(param->value);
+                                 result /= atom.val;
+                             }
+                         } else {
+                             result = 0;
+                         }
                      }
                      return std::make_shared<Value>(Atom(result));
                  });