#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n, nr;
bool  p[2000005];
int main()
{
	fin >> n;
	int i, j;
	i = 2;
	nr = 0;
	while ( i <= n)
	{
		if (p[i] == 0)
		{
			for (j = i * i; j <= n; j += i)
				p[j] = 1;
		}
		i++;
	}
	for (i = 2; i <= n; i++)
        if (p[i] == 0 )
            nr++;
	fout << nr << '\n';
	return 0;
}