mirror of
https://git.sb/baoshuo/OI-codes.git
synced 2024-12-25 17:12:02 +00:00
32 lines
649 B
C++
32 lines
649 B
C++
#include <bits/stdc++.h>
|
|
|
|
using namespace std;
|
|
|
|
int n, p, ans, mu[40005], primes[40005];
|
|
bool vis[40005];
|
|
|
|
int main() {
|
|
cin >> n;
|
|
if (!--n) {
|
|
cout << 0 << endl;
|
|
exit(0);
|
|
}
|
|
mu[1] = 1;
|
|
for (int i = 2; i <= n; i++) {
|
|
if (!vis[i]) {
|
|
primes[++p] = i;
|
|
mu[i] = -1;
|
|
}
|
|
for (int j = 1; i * primes[j] <= n; j++) {
|
|
vis[i * primes[j]] = true;
|
|
if (i % primes[j] == 0) break;
|
|
mu[i * primes[j]] = -mu[i];
|
|
}
|
|
}
|
|
for (int i = 1; i <= n; i++) {
|
|
ans += mu[i] * pow(n / i, 2);
|
|
}
|
|
cout << ans + 2 << endl;
|
|
return 0;
|
|
}
|