#include <algorithm>
#include <bitset>
#include <fstream>
using namespace std;
#define dim 2000001
//char v[dim];

bitset <dim> v;

int main()
{
	long long unsigned n, i, j, f=1;
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	
	fin>>n;
	
	for(i=2;i<n;++i)
	{
		++i;
		if(v[i]==0)
		{
			++f;
	
			for(j=i;j<=n/i;++j)
			{
				v[j*i]=1;
				++j;
			}
		}
	}
		
		fout<<f ;
		return 0;
}