题目：https://www.luogu.com.cn/problem/U448928 $80pts$ 其余两个测试点 TLE。
代码：

#include <bits/stdc++.h>
#define int long long
using namespace std;
int N, sum;
bool f;

signed main() {
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	cin >> N;
	for (int i = 2; i <= N; i ++) {
		f = 0;
		for (int j = 2; j <= sqrt(N); j ++) {
			if (i % j == 0) {
				sum += j;
				f = 1;
				break;
			}
		}
		if (f == 0) {
			sum += i;
		}
	}
	cout << sum;
	return 0;
}