def range_overlap(ranges):
    """Return common overlap among a set of [left, right] ranges."""
    lefts = []
    rights = []
    if ranges:
        for (left, right) in ranges:
            lefts.append(left)
            rights.append(right)

        max_left = max(lefts)
        min_right = min(rights)
        if min_right - max_left >= 1:
            return (max_left, min_right)