#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <iomanip>
#include <array>
#include <numeric>
#include <regex>
#include <bitset>
#include <deque>

using namespace std;
typedef long long ll;
typedef pair<int, int> p_ii;
#define REP(i,m,n) for(int i=(int)m ; i < (int) n ; ++i )
#define rep(i,n) REP(i,0,n)

const int INF = 1e9;
const double PI = acos(-1.0);
const ll MOD = 1e9 + 7;

bool is_prime[500100];
int prime[500100];
int cnt[500100];
int ex_max = -1;

void sieve() {
	int p = 0;
	rep(i, 500000)is_prime[i] = true;
	is_prime[0] = is_prime[1] = false;
	REP(i, 2, 500000) {
		if (is_prime[i]) {
			prime[p++] = i;
			for (int j = 2 * i; j <= 500000; j += i) is_prime[j] = false;
		}
	}
}

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

	ll res = 0;
	sieve();
	cnt[prime[0] + prime[1]]++;
	ex_max = max(ex_max, prime[0] + prime[1]);

	for (int i = 2; prime[i] <= n; i++) {
		for (int j = i + 1; prime[j] - prime[i] <= ex_max; j++) {
			res += (ll)cnt[prime[j] - prime[i]];
		}
		for (int j = 0; j < i; j++) {
			cnt[prime[j] + prime[i]]++;
		}
		ex_max = max(ex_max, prime[i] + prime[i - 1]);
	}

	cout << res << endl;

	return 0;
}