public static IntList addEmUp(IntList N1, IntList N2, int c) {
    if (N2 == null) {
        if (N1 == null) {
            if (c== 0) {
                return null ;
            } else {
                return new IntList(1, null) ;
            }
        } else {
            if (c==0) {
                return N1 ;
            } else {
                return addEmUp(null, N1, c) ;
            }
        }
    } else     /* N2 != null */ {
        int loD1 ;      // low digit of N1
        int loD2 ;      // low digit of N2
        IntList hiN1 ;  // high digits of N1
        IntList hiN2 ;  // high digits of N2
        if (N1 == null) {
            loD1 = 0 ;
            hiN1 = null ;
        } else {
            loD1 = N1.getItem() ;
            hiN1 = N1.getNext() ;
        }
        loD2 = N2.getItem() ;
        hiN2 = N2.getNext() ;
        int cOut = (loD1 + loD2 + c)/10 ;
        int sOut = (loD1 + loD2 + c)%10 ;
        IntList upperPart = addEmUp(hiN1, hiN2, cOut) ;
        return new IntList(sOut, upperPart) ;
    }
}