import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Question4 {
	// possible issue: we are assuming s is not null
	public static String findStudentIds(String s){
		StringBuilder sb = new StringBuilder();
		Pattern p = Pattern.compile("\\b[sS]\\d{7}\\b");
		Matcher m = p.matcher(s);
		while (m.find()) {
			sb.append(m.group());
			sb.append(',');
		}
		if (sb.length() > 0) {
			sb.setLength(sb.length() - 1);//lose the trailing comma
		}
		return sb.toString();
	}
	
	public static void main(String[] args){
		//String s = "s9782647_S9782647 and especially s0000001 but never s876.";
		String s = "s9782647 and S9782647 and especially s0000001 but never s876.";
		System.out.println(findStudentIds(s));		
	}

}