def solve(h, n, triangles, visited):
    if visited[h]:
        return False

    if h == 0:
        return True

    if n >= len(triangles):
        return False

    if h & triangles[n] == triangles[n]:
        if solve(h & ~triangles[n], n + 1, triangles, visited):
            return True

    if solve(h, n + 1, triangles, visited):
        return True

    visited[h] = True

    return False

def main():
    m = int(input())
    while m != 0:
        names = dict()
        edges = set()
        for _ in range(m):
            a, b = input().split()
            if a not in names:
                names[a] = len(names)
            if b not in names:
                names[b] = len(names)

            edges.add((names[a], names[b]))
            edges.add((names[b], names[a]))

        triangles = [(1 << a) + (1 << b) + (1 << c) for a in range(15) for b in range(a + 1, 15) if (a, b) in edges for c in
                 range(b + 1, 15) if
                 (a, c) in edges and (c, b) in edges]

        m = int(input())
        visited = [False]*(1<<len(names))
        if solve((1 << len(names)) - 1, 0, triangles, visited):
            print('possible')
        else:
            print('impossible')


if __name__ == '__main__':
    main()