/*
 * Sometimes the absurdly simple simply gets overlooked.
 *
 * This variant courtesy of christian.bau@cbau.freeserve.co.uk
 * (this is actually the second, faster one).
 *
 * A fix was required.
 */

#include <iostream>

unsigned long long pi(unsigned long long x)
{
	unsigned long long i, j, k, sum;

	for(i=2,sum=0;i<=x;++i,sum+=k)
	{
		for(j=2, k=1; j*j<=i; ++j)
		{
			if(i%j==0) { k=0; break; }
		}
	}

	return sum;
}