#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

/*
10
3
11

4
2
5
*/

const int MAX_N = 1e6 + 10;
int N = 0;

bool is_prime[MAX_N + 1];
void sieve(int n) {
    fill(is_prime, is_prime + n + 1, true);
    is_prime[0] = is_prime[1] = false;
    for (int i = 2; i * i <= n; i++) {
        if (is_prime[i]) {
            for (int j = 2 * i; j <= n; j += i) {
                is_prime[j] = false;
            }
        }
    }
}

void solve() {
    int res = 0;
    for (int i = 2; i <= N; i++) {
        if (is_prime[i]) {
            res++;
        }
    }

    printf("%d\n", res);
}

int main() {
    sieve(MAX_N);
    while (scanf("%d", &N) != EOF) {
        solve();
    }

    return 0;
}

