import java.io.*;
import java.sql.*;
import java.util.*;

public class GPA {
    private final static Map<String, Double> map = new HashMap<>();
	public static void main(String args[]) throws Exception {
        if (args.length != 1) {
            System.out.println("[Usage]: java GPA [query]");
            System.exit(0);
        }
        map.put("A+", 4.3);
        map.put("A", 4.0);
        map.put("A-", 3.7);
        map.put("B+", 3.3);
        map.put("B", 3.0);
        map.put("B-", 2.7);
        map.put("C+", 2.3);
        map.put("C", 2.0);
        map.put("C-", 1.7);
        map.put("F", 0.0);
		Class.forName("org.sqlite.JDBC");
		String url = "jdbc:sqlite:/Users/host/Documents/Personal/Courses.db";
		Connection con = DriverManager.getConnection(url);
		Statement stm = con.createStatement();
		ResultSet rs = stm.executeQuery(args[0]);
        double sum = 0;
        int credits = 0;
		while (rs.next()) {
            String grades = rs.getString("成績");
            if (!map.keySet().contains(grades))
                continue;
            sum += map.get(grades) * rs.getInt("學分");
            credits += rs.getInt("學分");
		}
        System.out.println(sum / credits);
        con.close();
	}
}