	static const int N = 999999;
	vector<bool> isp(N+1, true);
	vector<int> ps;
	for(int p=2; p<=N; ++p)
		if( isp[p] ) {
			ps.push_back(p);
			for(int q=p+p; q<=N; q+=p)
				isp[q] = false;
		}
