#include<fstream>
#include<vector>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int NMAX = 1 << 17;

int main() {

	int N, j, nrprime = 1;
	in>>N;
	vector<bool>V(N+1);
	for(long i=3;i<=N;i+=2)
	{
	    if(V[i]) continue;
	    for(long j=i+(i<<1);j<=N;j+=i<<1)
            V[j]=true;
        nrprime++;
	}
	out<<nrprime;

	return 0;
}