def merge_all_intersecting(sets):
    # merge all (i, end) sets  into i-th set for all possible i indices
    for i in range(len(sets) - 2, -1, -1): 
        # invariant: (i, end) sets are disjoint
        for j in range(len(sets) - 1, i, -1):
            if not sets[i].isdisjoint(sets[j]):  # intersecting sets
                sets[i].update(sets[j])  # merge j-th into i-th set
                sets.pop(j)  # remove merged set
 
 
sets = eval(input())
merge_all_intersecting(sets)
print(sets)

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WyB7MSwgMn0sIHsyLCAzfSwgezMsIDR9LCB7MTAsIDExLCAxMn0sIHsxMCwgMTN9LCB7MjAsIDIxfSBd

[ {1, 2}, {2, 3}, {3, 4}, {10, 11, 12}, {10, 13}, {20, 21} ]