Amdahl's law, measured

A pipeline has a parallelizable part P and a serial fraction S (S + P = 1). Implement static double Speedup(double serialFraction, int cores) returning Amdahl's speedup S(n) = 1 / (S + P/n) — and static int BreakEvenCores(double serialFraction, double minSpeedup) returning the smallest core count whose speedup reaches minSpeedup (return -1 if no finite core count reaches it). The test checks the hard ceiling: with 10% serial work, no number of cores beats 10x.