package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	reader := bufio.NewReader(os.Stdin)

	fmt.Print("Score (0-100): ")
	text, _ := reader.ReadString('\n')
	score, _ := strconv.Atoi(strings.TrimSpace(text))

	switch {
	case score >= 90:
		fmt.Println("Grade: A")
	case score >= 80:
		fmt.Println("Grade: B")
	case score >= 70:
		fmt.Println("Grade: C")
	case score >= 60:
		fmt.Println("Grade: D")
	default:
		fmt.Println("Grade: F")
	}
}