#include<bits/stdc++.h>
using namespace std;

const int maxn = 1e6 + 2;
bool ciur[maxn];
int main(){
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	ciur[0] = ciur[1] = true;
	int rs = 0;
	int n;
	cin >> n;
	for (int i = 2; i < n; i++){
		if (ciur[i] == false){
			rs+=1;
			for (int j = i * 2; j < n; j+=i){
				ciur[j] = true;
			}
		}
	}
	
	cout << rs;
	return 0;
}