66 lines
1.1 KiB
C++
66 lines
1.1 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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typedef unsigned long long ull;
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vector<ull> primes(ull maxPrime){
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vector<bool> p(maxPrime + 1, true);
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for(ull i = 2; i <= sqrt(maxPrime + 1); ++i){
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if(p[i]){
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for(ull j = i * 2; j < maxPrime + 1; j += i){
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p[j] = false;
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}
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}
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}
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vector<ull> result;
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for(ull i = 2; i < maxPrime + 1; ++i){
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if(p[i]){
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result.push_back(i);
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}
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}
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return result;
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}
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int main(){
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ios::sync_with_stdio(0);
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cin.tie(0);
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ull n;
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cin >> n;
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ull topPrime = ceil(cbrt(ceil(n / 2)));
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auto ps = primes(topPrime);
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ull result = 0;
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if(ps.size() < 2){
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cout << result << endl;
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cout << flush;
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return 0;
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}
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for(size_t i = 1; i < ps.size(); ++i){
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ull q = ps[i];
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for(size_t j = 0; j < i; ++j){
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ull p = ps[j];
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ull k = p * q * q * q;
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if(k > n){
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break;
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}
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result++;
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}
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}
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cout << result << endl;
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cout << flush;
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return 0;
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} |