package main

import (
  "errors"
  "fmt"
)

func validate(input int) error {

  if input < 0 {
    return errors.New("input can't be a negatice number")
  } else if input > 100 {
    return errors.New("input can't be over 100")
  } else if input%7 == 0 {
    return errors.New("input can't be divisible by 7")
  } else {
    return nil
  }

}

func main() {

  input := 21

  if err := validate(input); err != nil {
    fmt.Println(err)
  } else if input%2 == 0 {
    fmt.Println(input, "is even")
  } else {
    fmt.Println(input, "is odd")
  }

}