package main

import (
	"fmt"
	"strconv"
	"go.uber.org/zap/buffer"
)

func addCommas(n int) string {
    str := strconv.Itoa(n)
    
    // Add commas from right to left
    var result buffer.Buffer
    for i := range str {
        if i > 0 && (len(str)-i)%3 == 0 {
				 fmt.Fprint(&result,",")
        }
        result.WriteByte(str[i])
    }
    
    return result.String()
}

func main() {
    numbers := []int{12345, 1234567, 987654321, 12345, 123, 0}
    
    for _, num := range numbers {
        fmt.Printf("%d -> %s\n", num, addCommas(num))
    }
}