Connect cities

n, m = map(int, input().split())
roads = [tuple(map(int, input().split())) for _ in range(m)]

chunk_counter = 0
chunks = {}
chunk_roads = {}
for road_a, road_b in roads:
    if road_a not in chunks and road_b not in chunks:
        chunk_counter += 1
        chunks[road_a] = chunk_counter
        chunks[road_b] = chunk_counter
        
        chunk_roads[chunk_counter] = [road_a, road_b]
    elif road_a in chunks and road_b not in chunks:
        chunks[road_b] = chunks[road_a]

        chunk_roads[chunks[road_a]].append(road_b)
    elif road_b in chunks and road_a not in chunks:
        chunks[road_a] = chunks[road_b]

        chunk_roads[chunks[road_b]].append(road_a)
    else:
        raise Exception('duplicate road definition..>?')

print(chunk_counter)
for i in range(1, len(chunk_roads.keys())):
    print(chunk_roads[i][0], chunk_roads[i + 1][0])

Test 1

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 2

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 3

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 4

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 5

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 6

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 7

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 8

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 9

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 10

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 23, in <module>
    r...