diff --git a/Dockerfile b/Dockerfile
index d6f6ece..cb1b009 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,11 +1,11 @@
 FROM gcc:latest
 
+RUN g++ src/*.cpp -o Bowling
+
 WORKDIR /app
 
 COPY rolls.txt /app/
-COPY include/* /app/include/
-COPY src/* /app/src/
 
-RUN g++ src/*.cpp -o Bowling
+#RUN g++ src/*.cpp -o Bowling
 
 CMD ["./Bowling", "rolls.txt"]
diff --git a/rolls.txt b/rolls.txt
index 083bc71..aadbdc8 100644
--- a/rolls.txt
+++ b/rolls.txt
@@ -1 +1 @@
-2, 3, 5, 4, 9, 1, 2, 5, 3, 2, 4, 2, 3, 3, 4, 6, 10, 3, 2,
+2, 3, 5, 4, 9, 1, 2, 5, 3, 2, 4, 2, 3, 3, 4, 6, 10, 3, 2
diff --git a/src/NumberHelper.cpp b/src/NumberHelper.cpp
index d13a7f5..07b4230 100644
--- a/src/NumberHelper.cpp
+++ b/src/NumberHelper.cpp
@@ -1,4 +1,5 @@
 #include "../include/NumberHelper.h"
+#include <iostream>
 #include <string>
 #include <sstream>
 #include <vector>
@@ -17,8 +18,24 @@ vector<int> NumberHelper::getRolls(string csv){
 }
 
 bool NumberHelper::validateRolls(vector<int> rolls){
-    for(int i = 0; i < rolls.size(); ++i) {
+    int rollCount = rolls.size();
+    
+    for(int i = 0; i < rollCount; ++i) {
         if(rolls[i] > 10 || rolls[i] < 0) {
+            cerr << "Number: " << rolls[i] << " is invalid.";
+            return false;
+        }
+    }
+    
+    // A game can not have less than 12 rolls, and more than 21.
+    if (rollCount < 12 || rollCount > 21) {
+        cerr << "Incorrect amount of rolls.";
+        return false;
+    }
+    
+    // 10th frame rule.
+    if (rollCount == 21) {
+        if (rolls[18] != 10 && rolls[18] + rolls[19] != 10) {
             return false;
         }
     }
diff --git a/src/main.cpp b/src/main.cpp
index edc4b39..04d7af2 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -23,7 +23,6 @@ int main(int argc, char *argv[]) {
     vector<int> rolls = NumberHelper::getRolls(file);
     
     if (!NumberHelper::validateRolls(rolls)) {
-        cerr << "Non-valid number in rolls.";
         return 0;
     }