#include <iostream>
#include <cstring>
using namespace std;

bool is_prime[1000000];
int number[1000000] = {0};
void init_prime() {
    memset(is_prime, true, 1000000);
    for (int i = 2; i <= 999999; i++) {
        if (is_prime[i]) {
            number[i] = number[i-1]+1;
            for (int j = 2*i; j <= 999999; j+=i)
                is_prime[j] = false;
        } else
            number[i] = number[i-1];
    }
}

int main() {
    init_prime();

    int n;
    while (cin >> n) {
        cout << number[n] << endl;
    }
    return 0;
}