| Prepaid expenses and other current assets |
4. Prepaid expenses and other current assets Prepaid expenses and other current assets consist of the following: | | | | | | | | | As of | | | | | December 31, | | As of December 31, | | | 2024 | | 2025 | | 2025 | | | RMB | | RMB | | US$ | Prepaid expenses(1) | | 10,679,051 | | 21,414,229 | | 3,062,194 | Input VAT to be deducted | | 17,918,681 | | 14,090,676 | | 2,014,940 | Others | | 5,480,762 | | 8,041,902 | | 1,149,977 | Total prepaid expenses and other current assets | | 34,078,494 | | 43,546,807 | | 6,227,111 |
| (1) | Prepaid expenses mainly relate to prepaid service fee to the Group’s service providers. |
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