#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>

#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <deque>
#include <queue>
#include <stack>

using namespace std;

typedef long long ll;

//computes the chiur of Eratosthenes for finding the prime numbers
vector<bool> computePrimes(const int& n) {
    vector<bool> isPrime(n + 1, 1);
    isPrime[0] = isPrime[1] = 0;
    for (int i = 2; i * i <= n; ++i) {
        if (isPrime[i]) {
            int multiple = 2 * i;
            while (multiple <= n) {
                isPrime[multiple] = 0;
                multiple += i;
            }
        }
    }
    return isPrime;
}
void Solve() {
    int n, ans = 0;
    scanf_s("%d", &n);
    auto isPrime = computePrimes(n);
    for (int i = 2; i <= n; ++i) {
        ans += isPrime[i];
    }
    printf("%d\n", ans);
}

int main() {

    ios_base::sync_with_stdio(false);

    FILE* stream;
    freopen_s(&stream, "ciur.in", "r", stdin);
    freopen_s(&stream, "ciur.out", "w", stdout);

    Solve();

    return 0;
}