int eval(String s) {
		List<String> rel=new ArrayList<>();
		//0 : operator 1: numbers
		for (int i=0, n=s.length();i<n;) {
			if (rel.size()==0||rel.get(rel.size()-1).charAt(0)=='0') {
				int j=i+1;
				while (j<n&&Character.isDigit(s.charAt(j)))++j;
				rel.add("1,"+s.substring(i,j));
				i=j;
			} else {
				rel.add("0,"+s.substring(i,i+1));
				++i;
			}
		}
		return evaluateInorder(rel);
	}