diff --git a/aoc/04.cpp b/aoc/04.cpp
new file mode 100644
index 0000000..88449cd
--- /dev/null
+++ b/aoc/04.cpp
@@ -0,0 +1,67 @@
+#include <iostream>
+#include <fstream>
+#include <regex>
+
+using namespace std;
+
+// Advent of Code 2023, Day 4
+
+int main() {
+    ifstream input("input.txt");
+
+    int sums;
+    for (string line; getline(input, line);) {
+        regex e("Card\\s*[0-9]+: (.*)");
+        smatch m;
+
+        if (!regex_search(line, m, e) && m.size() <= 1) continue;
+
+        string set = m.str(1) + " ";
+
+        string currentNumber;
+        vector<int> winning;
+        vector<int> guesses;
+
+        bool buildMode = false;
+        bool guessing = false;
+        for (char current : set) {
+            if (current == '|') {
+                guessing = true;
+                continue;
+            }
+
+            if (isdigit(current)) {
+                currentNumber.push_back(current);
+                buildMode = true;
+                continue;
+            }
+
+            if (buildMode && current == ' ') {
+                if (guessing) {
+                    guesses.push_back(stoi(currentNumber));
+                } else {
+                    winning.push_back(stoi(currentNumber));
+                }
+                currentNumber = "";
+                buildMode = false;
+            }
+        }
+
+        int winningNums = 0;
+        for (auto item : winning) {
+            if (std::find(guesses.begin(), guesses.end(), item) != guesses.end()) {
+                if (winningNums == 0) {
+                    winningNums = 1;
+                    continue;
+                }
+                winningNums *= 2;
+            }
+        }
+
+        cout << line << " ["  << winningNums << "]" << endl;
+
+        sums += winningNums;
+    }
+
+    cout << endl << "Sum: " << sums;
+}
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