Initial Days

Day3/Program.cs

@@ -0,0 +1,25 @@
+using System.Text.RegularExpressions;
+// string input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))";
+string input = File.ReadAllText("input.txt").ReplaceLineEndings("");
+int total = 0;
+
+Regex valid = new Regex("mul\\((?<x>[0-9]+),(?<y>[0-9]+)\\)");
+Regex dontandDo = new Regex("(don\\'t\\(\\).*?do\\(\\))");
+
+input = dontandDo.Replace(input, "");
+
+List<(int x, int y)> multiplies = new();
+
+foreach (Match match in valid.Matches(input))
+{
+    string x = match.Groups["x"].Value;
+    string y = match.Groups["y"].Value;
+    multiplies.Add((int.Parse(x), int.Parse(y)));
+}
+
+foreach ((int x, int y) in multiplies)
+{
+    total += x * y;
+}
+
+Console.WriteLine(total);