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@@ -0,0 +1,36 @@
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+#include<bits/stdc++.h>
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+
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+using namespace std;
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+using LL=long long;
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+const int MAXN = 1e6 + 10;
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+vector<int> primes = {2, 3};
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+
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+void init() {
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+ for (int k = primes.back()+2; k <= MAXN; k += 2) {
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+ bool flag = true;
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+ for (auto p:primes) {
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+ if (p * p > k)break;
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+ if (k % p == 0) {
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+ flag = false;
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+ break;
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+ }
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+ }
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+ if (flag)primes.push_back(k);
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+ }
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+}
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+
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+int main() {
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+ init();
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+ for (int n; cin >> n;) {
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+ int tot = 0;
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+ for (size_t i = 0; i < primes.size() - 1; i++) {
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+ if (primes[i + 1] > n)break;
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+ if (primes[i + 1] - primes[i] <= 2) {
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+ //cout << primes[i] << " " << primes[i + 1] << endl;
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+ ++tot;
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+ }
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+ }
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+ cout << tot << endl;
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+ }
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+ return 0;
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+}
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