public class calc {
	public calc(){
	}

	public long add(long a, long b){
		return a + b ;
	}

	public double add(double a, double b){
		return a + b ;
	}

	public String add(String a, String b){
		if ((a == null)||(b == null)){
			return null ;
		}

		Double ret = new Double(Double.parseDouble(a) + Double.parseDouble(b)) ;
		return ret.toString() ;
	}

	public num add(num a, num b){
		if ((a == null)||(b == null)){
			return null ;
		}
		return new num(a.get_n() + b.get_n()) ;
	}

	public long div(long a, long b){
		return a / b ;
	}
}