#include <iostream>
#include <set>
#include <cmath>

using namespace std;

int main() {
    int n;
    cin >> n;
    int count = 0;
    for (int i = 1; i <= n; i++) {
        set<int> factors;
        for (int j = 1; j <= sqrt(i); j++) {
            if (i % j == 0) {
                factors.insert(j);
                factors.insert(i/j);
            }
        }
        if (factors.size() % 2 == 1) {
            count++;
        }
    }
    cout << count << endl;
    return 0;
}

#include 
#include 
#include 

using namespace std;

int main() {
    int n;
    cin >> n;
    int count = 0;
    for (int i = 1; i <= n; i++) {
        set factors;
        for (int j = 1; j <= sqrt(i); j++) {
            if (i % j == 0) {
                factors.insert(j);
                factors.insert(i/j);
            }
        }
        if (factors.size() % 2 == 1) {
            count++;
        }
    }
    cout << count << endl;
    return 0;
}

已AC

謝謝