#include <fstream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

const string IN_FILE = "ciur.in";
const string OUT_FILE = "ciur.out";

int countPrimes(const int n) {
    int primeCount = 1;
    auto isPrime = vector<bool>(n + 1, true);
    for (int i = 3; i <= n; i += 2) {
        if (isPrime[i]) {
            primeCount++;
            for (int j = min(1LL * n + 1, 1LL * i * i); j <= n; j += i) {
                isPrime[j] = false;
            }
        }
    }
    return primeCount;
}

int readInput() {
    ifstream in(IN_FILE);
    int n;
    in >> n;
    in.close();
    return n;
}

void writeOutput(const int count) {
    ofstream out(OUT_FILE);
    out << count << "\n";
    out.close();
}

int main() {
    const int n = readInput();
    const int count = countPrimes(n);
    writeOutput(count);
    return 0;
}