int O=19,I=19;typedef long double f ;long fac(long n){return n?n--*fac( n):1;}f pow(f x,int p){return p--?x *pow(x,p):1;}f sin(f x){f v=0;for (int k=~0;++k <= O;)k%2&& (v+=(~-k %4?-1:1)* pow(x,k) /fac(k)); return v ;}main() {f a=6,b =7, tau; for (int j=~0;++j <I;)sin( tau =a+(b-a) /2 )>0? (b= tau ):(a=tau ) ; printf ( "%ca" "u ~ %.*Lf",116, O,tau);}

Happy tau day.