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Risks and Concentration (Tables)
12 Months Ended
Dec. 31, 2020
Risks and Uncertainties [Abstract]  
Schedule of accounts receivable
   As of December 31, 
   2019   2020 
Receivables from Franchisee A   11%   19%
Receivables from Franchisee B   11%   19%
Receivables from Franchisee C   *    19%
Receivables from Franchisee D   *    11%
Receivables from Franchisee E   13%   * 
Receivables from Franchisee F   15%   - 
*Less than 10%