Summary of significant accounting policies (Details 3)	6 Months Ended
Jun. 30, 2025 USD ($)	Jun. 30, 2025 CNY (¥)	Jun. 30, 2024 CNY (¥)
Total revenues	$ 26,277,782	¥ 188,112,127	¥ 290,441,871
Mainland PRC [Member]
Total revenues	19,948,077	142,800,304	239,512,194
Hong Kong Revenues [Member]
Total revenues	$ 6,329,705	¥ 45,311,823	¥ 50,929,677

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details