#include<fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[20005];
int main() {
	int k = 0;
	long long n;
	fin >> n;
	v[1] = 1;
	for (int i = 2; i <= n; i++) {
		if (v[i] == 0) {
			for (int j = i + i; j <= n; j += i)
				v[j] = 1;
		}
	}
	for (int i = 1; i <= n; i++) {
		if (v[i] == 0) k++;
	}
	fout << k;
}