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@@ -0,0 +1,32 @@
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+#include<bits/stdc++.h>
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+
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+using namespace std;
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+const int N = 1000000 + 10;
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+vector<int> v(1, 2);
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+
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+void init() {
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+ for (int i = 3; i <= N; i += 2) {
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+ bool flag = true;
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+ for (int j = 3; j * j <= i; j += 2) {
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+ if (i % j == 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)v.push_back(i);
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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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+ int n;
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+ cin >> n;
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+ int tot = 0;
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+ for (int i = 0; i < v.size() - 1 && v[i + 1] <= n; i++) {
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+ if (v[i + 1] - v[i] <= 2) {
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+ ++tot;
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+ }
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+ }
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+ cout << tot << endl;
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+ return 0;
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+}
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