#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
 
int n, ciuc[2000001], prime;
int main() {
	fin >> n;
	for(int i = 2; i <= n; ++i)
	   ciuc[i] = 1;
	 for(int i = 2; i <= n; ++i) {
	 	 if (ciuc[i]) {
	 	 	 ++prime;
	 	 	 for(int j = i + i; j <= n; j+=i)
	 	 	     ciuc[j] = 0;
	 	 }
	 }
	 fout << prime - 1;
}