diff --git a/Aufgabe 3/input_example.txt b/Aufgabe 3/input_example.txt
index 2e1a90a..b774ec9 100644
--- a/Aufgabe 3/input_example.txt	
+++ b/Aufgabe 3/input_example.txt	
@@ -1 +1 @@
-xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))
\ No newline at end of file
+xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))
\ No newline at end of file
diff --git a/Aufgabe 3/main.cpp b/Aufgabe 3/main.cpp
index 6a42d33..f9d2830 100644
--- a/Aufgabe 3/main.cpp	
+++ b/Aufgabe 3/main.cpp	
@@ -18,7 +18,21 @@ std::string readTextFromFile(const std::string& fileName) {
     return result;
 }
 
-std::vector<std::string> determineValidMuls(std::string& content) {
+int checkForSubstringBefore(std::string& content, const std::string substring, size_t startPosition) {
+    size_t pos = 0;
+    int previousOccurence = -1;
+    while ((pos = content.find(substring, pos)) != std::string::npos) {
+        if(pos > startPosition) {
+            return previousOccurence;
+        } else {
+            previousOccurence = pos;
+        }
+        pos += substring.length();
+    }
+    return previousOccurence;
+}
+
+std::vector<std::string> determineValidMuls(std::string& content, bool checkEnabled=false) {
     std::vector<std::string> validMuls;
 
     std::regex regex(R"(mul\(\d{1,3},\d{1,3}\))");
@@ -26,7 +40,19 @@ std::vector<std::string> determineValidMuls(std::string& content) {
     auto end = std::sregex_iterator();
 
     for(auto it = begin; it != end; ++it) {
-        validMuls.push_back(it->str());
+        if(checkEnabled) {
+            int dont_start = checkForSubstringBefore(content, "don't()", it->position());
+            int do_start = checkForSubstringBefore(content, "do()", it->position());
+
+            if(dont_start < 0) {
+                validMuls.push_back(it->str());
+            } else if(do_start > dont_start) {
+                validMuls.push_back(it->str());
+            }
+        } else {
+            validMuls.push_back(it->str());
+        }
+
     }
     return validMuls;
 }
@@ -54,14 +80,14 @@ int calcMultSum(std::vector<std::string>& validMuls) {
 
 int main() {
     std::string content = readTextFromFile("../input.txt");
-    std::cout << content << std::endl;
-
-    std::vector<std::string> validMuls = determineValidMuls(content);
-    for(const auto& mul : validMuls) {
-        std::cout << mul << std::endl;
-    }
+    std::vector<std::string> validMuls = determineValidMuls(content, false);
 
     int result = calcMultSum(validMuls);
     std::cout << "The correct Mult Result is: " << result << std::endl;
+
+    std::vector<std::string> validMulsWithChecks = determineValidMuls(content, true);
+
+    int resultWithChecks = calcMultSum(validMulsWithChecks);
+    std::cout << "The correct Mult Result with check is: " << resultWithChecks << std::endl;
     return 0;
 }