A wooden box excavated from Indus valley had an activity of $1.18 \times 10^{13}$ disintegration per minute per g of carbon. What is the approximate age of this civilisation? ($t_{1/2}$ of $^{14}C = 5770$ years, initial activity of living carbon $\approx 1.18 \times 10^{13}$ is implied to be lower but standard value for comparison)