float a,b,c;main(n){for(;n=scanf("%f%f",&a,&b)>0;printf("%.f\n",6.2832*c))for(b/=c=a;n<8e3;n+=2)c-=a*=(1-b*b)*n/~n/~n,a*=n;}
Note that non-ascii characters in the above source code will be escaped (such as \x9f).
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