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Summary of significant accounting policies (Details 4)
12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2024
CNY (¥)
Dec. 31, 2023
CNY (¥)
Dec. 31, 2022
CNY (¥)
Total revenues $ 75,327,948 ¥ 541,487,420 ¥ 580,016,414 ¥ 586,060,092
Mainland PRC [Member]        
Total revenues 57,699,003 414,763,523 540,294,309 448,978,186
HONG KONG        
Total revenues 17,628,945 126,723,897 29,612,277
International [Member]        
Total revenues ¥ 10,109,828 ¥ 137,081,906