#include <fstream>
#define MaxSize 2000000
using namespace std;

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

int nr(int n);

char p[MaxSize];
int main()
{
	int n;
	fin >> n;
	fout << nr(n);
	fin.close();
	fout.close();
	return 0;
}
int nr(int n)
{
	int i, j, nr = 0;
	for(i = 2; i <= n; ++i)
	{
		if(p[i] == 0)
		{
			nr++;
			for(j = i + i; j <= n; j += i )
				p[j] = 1;
		}
	}
	return nr;
}