#include <fstream>
#include <cmath>

using namespace std;

int n, ok, i, j, ri, prime;


int main(){
	
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	
	fin>>n;
	for (i=2;i<=n;i++) {
		ok = 1;
		ri = sqrt(i*1.0);
		for (j=2;j<=ri;j++)
			if (i%j == 0) {
				ok = 0;
				break;
			}
		if (ok)
			prime++;
	}
	fout<<prime<<"\n";
	return 0;
}