#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int n;
bool is_prime[300001];
int primes[100000];
int cnt[300001];
int max_exist = -1;

void setPrime() {
	for (int i = 2; i <= 3 * n; i++) is_prime[i] = true;
	for (int i = 2; i <= 3 * n; i++) {
		if (is_prime[i]) {
			for (int j = i * 2; j <= 3 * n; j += i) {
				is_prime[j] = false;
			}
		}
	}
	
	int id = 0;
	for (int i = 2; i <= 400000; i++) {
		if (is_prime[i]) primes[id++] = i;
	}
}

int main() {
	cin >> n;
	setPrime();
	
	long long ans = 0;
	
	cnt[primes[0] + primes[1]]++;
	max_exist = max(max_exist, primes[0] + primes[1]);
	
	for (int i = 2; primes[i] <= n; i++) {
		for (int j = i + 1; primes[j] - primes[i] <= max_exist; j++) {
			ans += cnt[primes[j] - primes[i]];
		}
		for (int j = 0; j < i; j++) {
			cnt[primes[j] + primes[i]]++;
		}
		max_exist = max(max_exist, primes[i] + primes[i-1]);
	}
	cout << ans << endl;
	
	return 0;
}