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def longest_interval_lists(m):
    heap = []
    for i,lst in enumerate(m):
        heapq.heappush(heap,(lst[0],i,0))
    
    mn,mx = heap[0][0],max(heap)[0]
    max_in_heap = mx
    while heap:
        x,index,i = heapq.heappop(heap)
        if i + 1 == len(m[index]): break
        heapq.heappush(heap, (m[index][i+1],index,i+1))
        if max_in_heap < m[index][i+1]:
            max_in_heap = m[index][i+1]
        if max_in_heap - x < mx - mn:
            mn,mx = x,max_in_heap
    return mn,mx