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Summary of significant accounting policies (Details 3)
12 Months Ended
Dec. 31, 2024
USD ($)
Dec. 31, 2024
CNY (¥)
Dec. 31, 2023
CNY (¥)
Dec. 31, 2022
CNY (¥)
Disaggregation of Revenue [Line Items]        
Total revenues $ 75,327,948 ¥ 541,487,420 ¥ 580,016,414 ¥ 586,060,092
Transferred at Point in Time [Member]        
Disaggregation of Revenue [Line Items]        
Total revenues 57,699,003 414,763,523 580,016,414 586,060,092
Transferred over Time [Member]        
Disaggregation of Revenue [Line Items]        
Total revenues $ 17,628,945 ¥ 126,723,897