def merge_overlapping_interval(interval):
    temp_tuple = interval[:]
    temp_tuple.sort(key=lambda interval: interval[0])
    merged = [temp_tuple[0]]
    for current in temp_tuple:
        previous = merged[-1]
        if current[0] <= previous[1]:
            previous[1] = max(previous[1], current[1])
        else:
            merged.append(current)
    return merged

print(merge_overlapping_interval([[-25, -14], [-21, -16], [-20, -15], [-10, -7], [-8, -5], [-6, -3], [2, 4], [2, 3], [3, 6], [12, 15], [13, 18], [14, 17], [22, 27], [25, 30], [26, 29]]))