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37 lines
790 B
C++
37 lines
790 B
C++
#include <iostream>
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#include <cstring>
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using std::cin;
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using std::cout;
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using std::endl;
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const int N = 1000005;
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long long l, r, cnt, primes[N], ans;
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bool vis[N];
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int main() {
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for (int i = 2; i <= 1000000; i++) {
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if (!vis[i]) {
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primes[++cnt] = i;
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for (int j = i; j <= 1000000; j += i) {
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vis[j] = true;
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}
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}
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}
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cin >> l >> r;
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memset(vis, 0x00, sizeof(vis));
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l = std::max(l, 2ll);
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for (int i = 1; i <= cnt; i++) {
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long long p = primes[i];
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for (long long j = std::max((l + p - 1) / p * p, p * 2); j <= r; j += p) {
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vis[j - l + 1] = true;
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}
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}
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for (int i = 1; i <= r - l + 1; i++) {
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if (!vis[i]) ans++;
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}
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cout << ans << endl;
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return 0;
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}
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