You are a helpful assistant. The assistant first thinks about the reasoning process in the mind and then provides the user with the answer. The reasoning process and answer must be formatted exactly as follows:
<think>
[your reasoning process here]
</think>
<answer>
[your answer here]
</answer>
You can choose to imitate the reasoning process of relevant algorithms or explore an appropriate solution on your own. DO NOT use code, and remember to focus on the logical flow.
system
You are required to solve the Travelling Salesman Problem for an undirected flight route network. Your objective is to determine the shortest possible route that visits each of the listed airports exactly once and returns to the starting point.

**Problem to Solve**

- Airports to visit: YZR, IZO, KCM, PPN, ESL, DIN, GJT, ISC, BSD
- Travel distances (in kilometers) between each pair of airports:
YZR to ESL: 8879
YZR to GJT: 2679
YZR to PPN: 4967
YZR to BSD: 13265
YZR to ISC: 6068
YZR to IZO: 11756
YZR to KCM: 9202
YZR to DIN: 13412
IZO to ESL: 9522
IZO to GJT: 9788
IZO to PPN: 15304
IZO to BSD: 4707
IZO to ISC: 10938
IZO to KCM: 10109
IZO to DIN: 4574
KCM to ESL: 3586
KCM to GJT: 11001
KCM to PPN: 11911
KCM to BSD: 7611
KCM to ISC: 3722
KCM to DIN: 8388
PPN to ESL: 12430
PPN to GJT: 5531
PPN to BSD: 17770
PPN to ISC: 9299
PPN to DIN: 17917
ESL to GJT: 10546
ESL to BSD: 8084
ESL to ISC: 4097
ESL to DIN: 8081
DIN to GJT: 12742
DIN to BSD: 1554
DIN to ISC: 9977
GJT to BSD: 12595
GJT to ISC: 8201
ISC to BSD: 9749
Please calculate the shortest tour and format your answer as follows: [Airport A, Airport B, Airport C, ..., Airport A]
user
{"directed": false, "multigraph": false, "graph": {}, "nodes": [{"name": "YZR", "id": 0}, {"name": "IZO", "id": 1}, {"name": "KCM", "id": 2}, {"name": "PPN", "id": 3}, {"name": "ESL", "id": 4}, {"name": "DIN", "id": 5}, {"name": "GJT", "id": 6}, {"name": "ISC", "id": 7}, {"name": "BSD", "id": 8}], "links": [{"weight": 8879, "source": 0, "target": 4}, {"weight": 2679, "source": 0, "target": 6}, {"weight": 4967, "source": 0, "target": 3}, {"weight": 13265, "source": 0, "target": 8}, {"weight": 6068, "source": 0, "target": 7}, {"weight": 11756, "source": 0, "target": 1}, {"weight": 9202, "source": 0, "target": 2}, {"weight": 13412, "source": 0, "target": 5}, {"weight": 9522, "source": 1, "target": 4}, {"weight": 9788, "source": 1, "target": 6}, {"weight": 15304, "source": 1, "target": 3}, {"weight": 4707, "source": 1, "target": 8}, {"weight": 10938, "source": 1, "target": 7}, {"weight": 10109, "source": 1, "target": 2}, {"weight": 4574, "source": 1, "target": 5}, {"weight": 3586, "source": 2, "target": 4}, {"weight": 11001, "source": 2, "target": 6}, {"weight": 11911, "source": 2, "target": 3}, {"weight": 7611, "source": 2, "target": 8}, {"weight": 3722, "source": 2, "target": 7}, {"weight": 8388, "source": 2, "target": 5}, {"weight": 12430, "source": 3, "target": 4}, {"weight": 5531, "source": 3, "target": 6}, {"weight": 17770, "source": 3, "target": 8}, {"weight": 9299, "source": 3, "target": 7}, {"weight": 17917, "source": 3, "target": 5}, {"weight": 10546, "source": 4, "target": 6}, {"weight": 8084, "source": 4, "target": 8}, {"weight": 4097, "source": 4, "target": 7}, {"weight": 8081, "source": 4, "target": 5}, {"weight": 12742, "source": 5, "target": 6}, {"weight": 1554, "source": 5, "target": 8}, {"weight": 9977, "source": 5, "target": 7}, {"weight": 12595, "source": 6, "target": 8}, {"weight": 8201, "source": 6, "target": 7}, {"weight": 9749, "source": 7, "target": 8}]}
You are required to solve the Travelling Salesman Problem for an undirected flight route network. Your objective is to determine the shortest possible route that visits each of the listed airports exactly once and returns to the starting point.

**Problem to Solve**

- Airports to visit: YZR, IZO, KCM, PPN, ESL, DIN, GJT, ISC, BSD
- Travel distances (in kilometers) between each pair of airports:
YZR to ESL: 8879
YZR to GJT: 2679
YZR to PPN: 4967
YZR to BSD: 13265
YZR to ISC: 6068
YZR to IZO: 11756
YZR to KCM: 9202
YZR to DIN: 13412
IZO to ESL: 9522
IZO to GJT: 9788
IZO to PPN: 15304
IZO to BSD: 4707
IZO to ISC: 10938
IZO to KCM: 10109
IZO to DIN: 4574
KCM to ESL: 3586
KCM to GJT: 11001
KCM to PPN: 11911
KCM to BSD: 7611
KCM to ISC: 3722
KCM to DIN: 8388
PPN to ESL: 12430
PPN to GJT: 5531
PPN to BSD: 17770
PPN to ISC: 9299
PPN to DIN: 17917
ESL to GJT: 10546
ESL to BSD: 8084
ESL to ISC: 4097
ESL to DIN: 8081
DIN to GJT: 12742
DIN to BSD: 1554
DIN to ISC: 9977
GJT to BSD: 12595
GJT to ISC: 8201
ISC to BSD: 9749
Please calculate the shortest tour and format your answer as follows: [Airport A, Airport B, Airport C, ..., Airport A]
test