def kVertexCover(G, n):
    rec = rec_kVertexCover(G, n, set())
    return set(rec)


def rec_kVertexCover(graph, k, visited):
    edgess = [a for y in graph.values() for a in y]
    edges = set(filter(lambda x: x not in visited, edgess))
    print(edgess)
    print(edges)
    print()
    if len(edges) == 0:
        print("GEVONDEN")
        return []
    if len(edges) / 2 > k:
        return None
    edge = None
    for key in graph.keys:
        for el in graph[key]:
            if key not in visited and el not in visited:
                edge = (key, el)
                break

    visited.add(edge[0])

    cover1 = rec_kVertexCover(graph, k - 1, visited)
    if cover1 is None:
        visited.remove(edge[0])
        visited.add(edge[1])
        cover2 = rec_kVertexCover(graph, k - 1, visited)
        if cover2 is None:
            visited.remove(edge[1])
            return None
        else:
            return cover2 + [edge[1]]
    else:
        return cover1 + [edge[0]]


# print(
#     kVertexCover({'A': ['B', 'E'], 'B': ['A', 'C', 'D', 'E', 'F'], 'C': ['B'], 'D': ['B'], 'E': ['A', 'B'], 'F': ['B']},
#                  2)
# )
print(kVertexCover({'A': ['B'], 'B': ['A', 'C'], 'C': ['B']}, 1))