calculate t1 = arcsin(output)
calculate t2 = pi - t1
solve linear cong: 10^299 * flag = t2 mod pi

https://gist.github.com/yytasbag/d75c679da6c452e4e12468c0b680b59b

Original writeup (https://gist.github.com/yytasbag/d75c679da6c452e4e12468c0b680b59b).