diff --git a/README.md b/README.md
new file mode 100644
index 0000000..c66d629
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+# domainer
diff --git a/domainer.go b/domainer.go
new file mode 100644
index 0000000..8371f87
--- /dev/null
+++ b/domainer.go
@@ -0,0 +1,45 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+func extractRootDomain(domain string) string {
+	parts := strings.Split(domain, ".")
+	if len(parts) < 2 {
+		return "none"
+	}
+	return strings.Join(parts[len(parts)-2:], ".")
+}
+
+func main() {
+	stat, _ := os.Stdin.Stat()
+	if (stat.Mode() & os.ModeCharDevice) != 0 {
+		fmt.Fprintln(os.Stderr, "Please provide domains via stdin.")
+		os.Exit(1)
+	}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	seenDomains := make(map[string]bool)
+
+	for scanner.Scan() {
+		domain := scanner.Text()
+		rootDomain := extractRootDomain(domain)
+		if rootDomain != "none" {
+			seenDomains[rootDomain] = true
+		}
+	}
+
+	if scanner.Err() != nil {
+		fmt.Fprintln(os.Stderr, "Error reading input:", scanner.Err())
+		os.Exit(1)
+	}
+
+	for domain := range seenDomains {
+		fmt.Println(domain)
+	}
+}
+
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..705d05e
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module github.com/topscoder/domainer
+
+go 1.20