23 lines
417 B
C++
23 lines
417 B
C++
#include <bits/stdc++.h>
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using namespace std;
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//判断一个数是不是质数
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bool isPrime(int n) {
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if (n < 2) return false;
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for (int i = 2; i <= n / i; i++)
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if (n % i == 0) return false;
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return true;
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}
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int ans;
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int main() {
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int n;
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cin >> n;
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for (int i = 7; i <= n; i++)
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if (i % 10 == 7 && isPrime(i)) ans++;
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cout << ans << endl;
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return 0;
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} |