#include <fstream>
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

const int MAX_SIZE = 2000000;
bool ciur[MAX_SIZE + 1];

int number_prime(int n) {
    int counter = 0;
    for (long long i = 2; i * i <= n; i++) {
        if (!ciur[i]) {
            for(long long j = i * i; j <= n; j += i) {
                ciur[j] = 1;
            }
        }
    }
    for (int i = 2; i <= n; ++i) {
        if (!ciur[i]) {
            ++counter;
        }
    }
    return counter;
}

int main() {
    int n;
    cin >> n;
    cout << number_prime(n);
    return 0;
}