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: PAG, WHK, CND, RVD, MSS, GKK, RVV, OSW, SIP
- Travel distances (in kilometers) between each pair of airports:
PAG to MSS: 14808
PAG to RVD: 20002
PAG to WHK: 8258
PAG to GKK: 6393
PAG to OSW: 10494
PAG to SIP: 9660
PAG to CND: 10322
PAG to RVV: 12242
WHK to MSS: 14917
WHK to RVD: 13398
WHK to GKK: 12369
WHK to OSW: 17917
WHK to SIP: 17020
WHK to CND: 17660
WHK to RVV: 5037
CND to MSS: 8557
CND to RVD: 11921
CND to GKK: 6817
CND to OSW: 3536
CND to SIP: 1996
CND to RVV: 18699
RVD to MSS: 9017
RVD to GKK: 16315
RVD to OSW: 13975
RVD to SIP: 12571
RVD to RVV: 12265
MSS to GKK: 14615
MSS to OSW: 9196
MSS to SIP: 8430
MSS to RVV: 11561
GKK to OSW: 8480
GKK to SIP: 6740
GKK to RVV: 16738
RVV to OSW: 18993
RVV to SIP: 18160
OSW to SIP: 2637
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": "PAG", "id": 0}, {"name": "WHK", "id": 1}, {"name": "CND", "id": 2}, {"name": "RVD", "id": 3}, {"name": "MSS", "id": 4}, {"name": "GKK", "id": 5}, {"name": "RVV", "id": 6}, {"name": "OSW", "id": 7}, {"name": "SIP", "id": 8}], "links": [{"weight": 14808, "source": 0, "target": 4}, {"weight": 20002, "source": 0, "target": 3}, {"weight": 8258, "source": 0, "target": 1}, {"weight": 6393, "source": 0, "target": 5}, {"weight": 10494, "source": 0, "target": 7}, {"weight": 9660, "source": 0, "target": 8}, {"weight": 10322, "source": 0, "target": 2}, {"weight": 12242, "source": 0, "target": 6}, {"weight": 14917, "source": 1, "target": 4}, {"weight": 13398, "source": 1, "target": 3}, {"weight": 12369, "source": 1, "target": 5}, {"weight": 17917, "source": 1, "target": 7}, {"weight": 17020, "source": 1, "target": 8}, {"weight": 17660, "source": 1, "target": 2}, {"weight": 5037, "source": 1, "target": 6}, {"weight": 8557, "source": 2, "target": 4}, {"weight": 11921, "source": 2, "target": 3}, {"weight": 6817, "source": 2, "target": 5}, {"weight": 3536, "source": 2, "target": 7}, {"weight": 1996, "source": 2, "target": 8}, {"weight": 18699, "source": 2, "target": 6}, {"weight": 9017, "source": 3, "target": 4}, {"weight": 16315, "source": 3, "target": 5}, {"weight": 13975, "source": 3, "target": 7}, {"weight": 12571, "source": 3, "target": 8}, {"weight": 12265, "source": 3, "target": 6}, {"weight": 14615, "source": 4, "target": 5}, {"weight": 9196, "source": 4, "target": 7}, {"weight": 8430, "source": 4, "target": 8}, {"weight": 11561, "source": 4, "target": 6}, {"weight": 8480, "source": 5, "target": 7}, {"weight": 6740, "source": 5, "target": 8}, {"weight": 16738, "source": 5, "target": 6}, {"weight": 18993, "source": 6, "target": 7}, {"weight": 18160, "source": 6, "target": 8}, {"weight": 2637, "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: PAG, WHK, CND, RVD, MSS, GKK, RVV, OSW, SIP
- Travel distances (in kilometers) between each pair of airports:
PAG to MSS: 14808
PAG to RVD: 20002
PAG to WHK: 8258
PAG to GKK: 6393
PAG to OSW: 10494
PAG to SIP: 9660
PAG to CND: 10322
PAG to RVV: 12242
WHK to MSS: 14917
WHK to RVD: 13398
WHK to GKK: 12369
WHK to OSW: 17917
WHK to SIP: 17020
WHK to CND: 17660
WHK to RVV: 5037
CND to MSS: 8557
CND to RVD: 11921
CND to GKK: 6817
CND to OSW: 3536
CND to SIP: 1996
CND to RVV: 18699
RVD to MSS: 9017
RVD to GKK: 16315
RVD to OSW: 13975
RVD to SIP: 12571
RVD to RVV: 12265
MSS to GKK: 14615
MSS to OSW: 9196
MSS to SIP: 8430
MSS to RVV: 11561
GKK to OSW: 8480
GKK to SIP: 6740
GKK to RVV: 16738
RVV to OSW: 18993
RVV to SIP: 18160
OSW to SIP: 2637
Please calculate the shortest tour and format your answer as follows: [Airport A, Airport B, Airport C, ..., Airport A]
test