#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    int n;
    cin >> n;

    int m = (int)sqrt(n);

    vector<bool> q(n + 1);
    for (int i = 2; i <= m; i++) {
        if (q[i]) continue;
        for (int j = i * i; j <= n; j += i) {
            q[j] = true;
        }
    }

    int r = 0;
    vector<int> p;
    int j = 0;
    int b = 1;
    for (int i = 3; i <= n; i += 2) {
        if (!q[i]) {
            while (j < p.size() && p[j] < i + 2) j++;
            if (j < p.size() && p[j] == i + 2) r++;
            if (b) {
                if (i * i - 2 > n) {
                    b = 0;
                    continue;
                }
                p.push_back(i * i);
            }
        }
    }

    cout << r * 2 + (n >= 2) << endl;

    return 0;
}