#include <cstdio>
#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <ctype.h>
#include <cstring>
#include <string>
#include <ctime>
#include <cassert>
#include <utility>

#define LIM 2000005

using namespace std;

bool viz[LIM];

int main() {
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out","w", stdout);

    int n, cnt = 0;

    cin >> n;

    for(int i = 2; i <= n; i++) {
        if(!viz[i]) {
            cnt++;
            if(i <= n / i) {
                for(int j = i * i; j <= n; j += i) {
                    viz[j] = true;
                }
            }
        }
    }

    cout << cnt << "\n";

	return 0;
}