Simplify calculation

src/targets/gpu/jit/concat.cpp

@@ -63,11 +63,7 @@ struct concat_compiler : compiler<concat_compiler>
 
     static std::size_t get_concat_elements(const std::vector<shape>& inputs)
     {
-        auto total =
-            std::accumulate(inputs.begin(), std::prev(inputs.end()), 0, [](auto x, auto s) {
-                return x + s.elements();
-            });
-        return total / (inputs.size() - 1);
+        return inputs.back().elements() / (inputs.size() - 1);
     }
 
     operation compile_op(context& ctx, const std::vector<shape>& inputs, const value& v) const