import java.util.*;

class IntSparseSet extends AbstractSet<Integer> {
    private int[] sparse, dense;
    private int shift, n = 0;

    private class SetIterator implements Iterator<Integer> {
        private int it = -1;

        public boolean hasNext() {
            return it < n - 1;
        }

        public Integer next() {
            return dense[++it] + shift;
        }

        public void remove() {
            IntSparseSet.this.remove(dense[it] + shift);
        }
    }

    public IntSparseSet(int a, int b) {
        shift = a; sparse = new int[b - a]; dense = new int[b - a];
    }

    public boolean add(Integer x) {
        if (x - shift >= 0 && x - shift < sparse.length && !contains(x)) {
            sparse[x - shift] = n; dense[n++] = x - shift;
            return true;
        }
        return false;
    }

    public boolean contains(Integer x) {
        return sparse[x - shift] < n && dense[sparse[x - shift]] == x - shift;
    }

    public int size() {
        return n;
    }

    public boolean remove(Object o) {
        Integer x = (Integer) o;
        if (x - shift >= 0 && x - shift < sparse.length && contains(x)) {
            dense[sparse[x - shift]] = dense[--n];
            sparse[dense[n]] = sparse[x - shift];
            return true;
        }
        return false;
    }

    public void clear() {
        n = 0;
    }

    public Iterator<Integer> iterator() {
        return new SetIterator();
    }
}