#include <iostream>
#include <fstream>

using namespace std;

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

int n, cnt, i, j;
char prime[2000005];

int main() {
    in >> n;
    for (i = 2; i <= n; ++i)
        prime[i] = 1;

    for (i = 2; i <= n; ++i)
        if (prime[i]) {
            ++cnt;

            for (j = i+i; j <= n; j += i)
                prime[j] = 0;
        }

    out << cnt;
    return 0;
}