#include <bits/stdc++.h>

using namespace std;

using ll = long long;

bool is_prime(int n) {
    if (n % 2 == 0) return false;
    for (int i = 2; i * i <= n; i++) {
        if (n % i == 0) return false;
    }
    return n != 1;
}

vector<int> divisor(int n) {
    vector<int> res;
    for (int i = 1; i * i <= n; i++) {
        if (n % i == 0) {
            res.emplace_back(i);
            if (i != n / i) res.emplace_back(n / i);
        }
    }
    return res;
}

map<int, int> prime_factor(int n) {
    map<int, int> res;
    for (int i = 2; i * i <= n; i++) {
        while (n % i == 0) {
            ++res[i];
            n /= i;
        }
    }
    if (n != 1) res[n] = 1;
    return res;
}

vector<int> sieve(int n) {
    //vector<int> res;
    vector<int> is_prime(n + 1, true);
    is_prime[0] = false;
    is_prime[1] = false;
    for (int i = 2; i <= n; i++) {
        if (!is_prime[i]) continue;
        //res.emplace_back(i);
        for (int j = 2 * i; j <= n; j += i) is_prime[j] = false;
    }
    return is_prime;//res;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    if (n == 1) {
        cout << 0 << endl;
        return 0;
    }

    int sq = 0;
    while (true) {
        int nex = sq + 1;
        if (nex * nex > n + 2) break;
        sq = nex;
    }

    vector<int> s = sieve(n);

    ll ans = 0;
    for (int i = 2; i <= sq; i++) {
        if (i > n) break;
        if (!s[i]) continue;
        int x = i * i - 2;
        if (x > n) break;
        if (!s[x]) continue;
        if (x == 2) ans++;
        else ans += 2;
    }
    cout << ans << endl;
    return 0;
}