JAVA科学记数法

import java.io.*;
import java.math.*;
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String str = in.readLine();
        BigDecimal db = new BigDecimal(str);
        System.out.println(db.toPlainString());
    }
}

因为用 Scanner 超时了