diff --git a/main.go b/main.go
new file mode 100644
index 0000000..5d74dc2
--- /dev/null
+++ b/main.go
@@ -0,0 +1,80 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+// environmental variable
+const nextwordDataPath = "NEXTWORD_DATA_PATH"
+
+// flags
+var dataPath = flag.String("data", os.Getenv(nextwordDataPath), "path to the data directory")
+var candidateNum = flag.Int("candidate-num", 100, "max candidates number")
+var helpFlag = flag.Bool("h", false, "show this message")
+var greedyFlag = flag.Bool("greedy", false, "show as many result as possible")
+
+func main() {
+	if err := run(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func run() error {
+	flag.Parse()
+
+	// help
+	if *helpFlag {
+		showHelpMessage()
+		return nil
+	}
+
+	// new nextword
+	params := &NextwordParams{
+		CandidateNum: *candidateNum,
+		Greedy:       *greedyFlag,
+	}
+	nw, err := NewNextword(*dataPath, params)
+	if err != nil {
+		return err
+	}
+
+	// loop
+	sc := bufio.NewScanner(os.Stdin)
+	for sc.Scan() {
+		candidates, err := nw.Suggest(sc.Text())
+		if err != nil {
+			return err
+		}
+		fmt.Println(strings.Join(candidates, " "))
+	}
+	if sc.Err() != nil {
+		return sc.Err()
+	}
+
+	return nil
+}
+
+func showHelpMessage() {
+	fmt.Fprintln(os.Stderr, "Nextword prints the most likely English words that follow the stdin sentence.")
+	fmt.Fprintln(os.Stderr)
+	flag.Usage()
+	fmt.Fprintln(os.Stderr)
+	fmt.Fprintln(os.Stderr, `You need to install nextword-data and set "NEXTWORD_DATA_PATH" environment variable.`)
+	fmt.Fprintln(os.Stderr, `It available at https://github.com/high-moctane/nextword-data`)
+	fmt.Fprintln(os.Stderr)
+	fmt.Fprintln(os.Stderr, `The result depends on whether the input string ends with a space character.`)
+	fmt.Fprintln(os.Stderr, `If the string does not end with a space, nextword will print candidate words which`)
+	fmt.Fprintln(os.Stderr, `begin the last word in the sentence.`)
+	fmt.Fprintln(os.Stderr)
+	fmt.Fprintln(os.Stderr, `Example:`)
+	fmt.Fprintln(os.Stderr, `	input:  "Alice was "`)
+	fmt.Fprintln(os.Stderr, `	output: "not a the in still born very so to beginning too at sitting ..."`)
+	fmt.Fprintln(os.Stderr)
+	fmt.Fprintln(os.Stderr, `	input:  "Alice w"`)
+	fmt.Fprintln(os.Stderr, `	output: "was would were went with will who wrote when wants ..."`)
+}