#include <bits/stdc++.h>
using namespace std;

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

const int N = 2000005;

bool c[N];

int n, ans;

int main() {
    fi >> n;

    c[0] = c[1] = 1;
    for (int i = 2; i * i <= n; ++i)
        for (int j = 2 * i; j <= n; j+= i)
            c[j] = 1;

    for (int i = 0; i <= n; ++i)
        if (c[i] == false)
            ans+= 1;

    fo << ans << '\n';

    return 0; }