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

vector<int64_t> sieve(int64_t n){
    vector<int64_t> ret;
    vector<bool> is_prime(n+1);
    for(int64_t i=2; i<=n; i++) is_prime[i] = true;
    for(int64_t i=2; i<=n; i++){
        if(is_prime[i]){
            ret.push_back(i);
            for(int64_t j=2*i; j<=n; j+=i) is_prime[j] = false;
        }
    }
    return ret;
}


int main(){
    int N;
    cin >> N;
    auto primes = sieve(N);
    set<int> pset;
    for(int p : primes) pset.insert(p);

    int ans = 0;
    if(N >= 2) ans++;
    for(int r : primes){
        if(r == 2) continue;
        if(pset.count(r*r - 2)) ans += 2;
        if(r*r - 2 >= N) break;
    }
    cout << ans << endl;
    return 0;
}