diff --git a/main.cpp b/main.cpp
index 947c3c4..a8ad0fe 100644
--- a/main.cpp
+++ b/main.cpp
@@ -238,7 +238,7 @@ vector<MyFunction> get_linear_combinations(const vector<MyFunction> &linear_comp
 }
 
 string preprocess_factor(string factor) {
-    if ( factor.find("+") != string::npos and factor.find("*") == string::npos )
+    if ( factor.find("+") != string::npos and factor.find("*") == string::npos and factor[0] !='(' and factor[factor.size() - 1] != ')')
         return "(" + factor + ")";
     return factor;
 }