#include<iostream>
#include<string>
#include<vector>
#include<deque>
using namespace std;

int main() {

    vector<bool> primes (1000000);
    for (int n = 0; n < 1000000; n++) {
        primes[n] = true;
    }
    primes[0] = false;
    primes[1] = false;

    for (int n = 2; n < 1000000; n++) {
        if (primes[n]) {
            for (int k = 2*n; k < 1000000; k = k+n) {
                primes[k] = false;
            }
        }
    }

    int n;
    while (cin >> n) {
        int result = 0;
        for(int i = 0; i <= n; i++) {
            if ( primes[i] ) {
                result += 1;
            }
        }
        cout << result << endl;
    }
     
    return 0;
}