#include <algorithm>

extern unsigned long primetab[];
extern unsigned long nprimetab;

unsigned long long pi(unsigned long long x)
{
	if(x >= 20000000)
		return 0; // blow up, but genteelly

	unsigned long * ptr = std::lower_bound(primetab, primetab + nprimetab, (unsigned long) x);

	return ptr - primetab;
}