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22 lines
425 B
C++
22 lines
425 B
C++
#include <bits/stdc++.h>
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using namespace std;
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int n, p, primes[1000005];
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bool not_prime[1000005];
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int main() {
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cin >> n;
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for (int i = 2; i <= n; i++) {
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if (!not_prime[i]) {
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primes[p++] = i;
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}
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for (int j = 0; primes[j] * i <= n; j++) {
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not_prime[primes[j] * i] = true;
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if (i % primes[j] == 0) break;
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}
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}
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cout << p << endl;
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return 0;
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}
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