#include #define rep(i,a,b) for(int i=a;i<(b);++i) #define erep(i,a,b) for(int i=a;i<=(int)(b);++i) #define per(i,a,b) for(int i=(a);i>(b);--i) #define eper(i,a,b) for(int i=(a);i>=b;--i) #define pb push_back #define mp make_pair #define INF (1<<30)-1 #define MOD 1000000007 #define all(x) (x).begin(),(x).end() #define vii vector #define vll vector using namespace std; typedef long long ll; typedef pair Pii; templatebool chmax(T &a, const T &b) { if (abool chmin(T &a, const T &b) { if (b makePrimes(int n) { vector res, pr(n + 1, 1); pr[0] = pr[1] = 0; rep(p, 2, sqrt(n) + 2) if (pr[p]) for (int x = p * 2; x <= n; x += p) pr[x] = 0; rep(p, 2, n + 1) if (pr[p]) res.push_back(p); return res; } int n, cnt[400001]; ll ans; int main() { cin.tie(0); ios::sync_with_stdio(false); cin >> n; auto primes = makePrimes(3 * n + 1); for (int i = 0; i < primes.size() && primes[i] <= n; ++i) { for (int j = primes.size() - 1; primes[j] > primes[i]; --j) ans += cnt[primes[j] - primes[i]]; rep(k, 0, i) cnt[primes[i] + primes[k]]++; } cout << ans << endl; return 0; }