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STOCKHOLDERS' EQUITY - Fair value assumptions of options (Details)
3 Months Ended
Mar. 31, 2019
Volatility, minimum 204.59%
Volatility, maximum 291.61%
Risk-free rate, minimum 2.40%
Risk-free rate, maximum 2.49%
Minimum [Member]  
Expected term (in years) 5 years
Maximum [Member]  
Expected term (in years) 6 years 3 months