#include <iostream>
#include <vector>
using namespace std;
int main(){
	int N;
	cin >> N;
	vector<bool> prime(N + 1, true);
	prime[0] = false;
	prime[1] = false;
	for (int i = 2; i <= N; i++){
		if (prime[i]){
			for (int j = i * 2; j <= N; j += i){
				prime[j] = false;
			}
		}
	}
	int ans = 0;
	if (N >= 2){
		ans++;
	}
	for (int i = 3; i * i <= N + 2; i++){
		if (prime[i] && prime[i * i - 2]){
			ans += 2;
		}
	}
	cout << ans << endl;
}