static abstract class Ab {
        final int y;
        public Ab(int x) {y = x;}
        protected abstract int f() throws IOException;
    }

    static interface Bb {
        abstract java.util.List<String> list(java.util.List<String> x);
        public abstract int f() throws CloneNotSupportedException;
    }

    static class ImplBb extends Ab implements Bb {
        ImplBb(int x) {
            super(x);
        }
        @Override
        public List<String> list(List<String> x) {
            return null;
        }


        public int f() {
            return 0;
        }
    }