#include <bits/stdc++.h>

using namespace std;

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

const int NMax = 2e6 + 50;

int ans;
bitset < NMax > ciur;

void Erathos(int n) {
	ans = 1;
	for(int i = 3; i <= n; i += 2) {
		if(ciur[i] == false) {
			++ans;

			for(int j = 3 * i; j <= n; j += 2 * i) {
				ciur[j] = true;
			}
		}
	}
}

int main() {
	
	int n;
	fin >> n;

	Erathos(n);

	fout << ans;	
	
	return 0;
}