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- #include<bits/stdc++.h>
-
- using namespace std;
- using LL=long long;
- const int MAXN = 1e6 + 10;
- vector<int> primes = {2, 3};
-
- void init() {
- for (int k = primes.back()+2; k <= MAXN; k += 2) {
- bool flag = true;
- for (auto p:primes) {
- if (p * p > k)break;
- if (k % p == 0) {
- flag = false;
- break;
- }
- }
- if (flag)primes.push_back(k);
- }
- }
-
- int main() {
- init();
- for (int n; cin >> n;) {
- int tot = 0;
- for (size_t i = 0; i < primes.size() - 1; i++) {
- if (primes[i + 1] > n)break;
- if (primes[i + 1] - primes[i] <= 2) {
- //cout << primes[i] << " " << primes[i + 1] << endl;
- ++tot;
- }
- }
- cout << tot << endl;
- }
- return 0;
- }
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