Extract

package com.company;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String input = br.readLine();
        StringBuilder sb = new StringBuilder();

        String regex = "^|\\s[a-z0-9][\\.\\_\\-a-z0-9]*[a-z0-9]@[a-z0-9][\\.\\-a-z0-9]*[a-z0-9]\\.[a-z]{2,}";
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(input);

        while (matcher.find()) {
            sb.append(matcher.group() + "\n");
        }

        System.out.println(sb.toString());
    }
}