#include<fstream>
#include<algorithm>
#include<queue>
#include<vector>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

bool D[2000010];



int main()
{
	unsigned long i,j, nr = 0, N;

	in >> N;

	for (i = 2;i <= N;++i)
	{
		if (!D[i])
		{
			++nr;

			for (j = i*i;j <= N;j+=i)
				D[j] = 1;

		}
	}

	out << nr;


}