package main

import (
    "net/http"
    "os"
    "fmt"
)

func indexHandler(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("<h1>Hello World!</h1>"))
}

func main() {
    port := os.Getenv("PORT")
    if port == "" {
        port = "3000"
    }

    fmt.Print("\nim run in http://127.0.0.1:", port)

    mux := http.NewServeMux()
    mux.HandleFunc("/", indexHandler)
    http.ListenAndServe(":"+port, mux)
}