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

public class LookAhead {

    public static void main(String[] args) {
        String regex = "(?=^91).*";
        
        Pattern p = Pattern.compile(regex);
        String no = "91.9789900009933";
        
        Matcher m = p.matcher(no);
        
        String phno = "not found";
        if (m.find()) {
            phno = m.group();
        }
        String msg = "Phone number is: " + phno;
        System.out.println(msg);
    }
}