Why???

#include<bits/stdc++.h>
using namespace std;
int n;
int a[10005];
int b[10005];
int main() {
	cin >> n;
	memset(a , 0x3f , sizeof(a));
	memset(a , 0x3f , sizeof(b));
	int ans = 0;
	for(int i = 1 ; i <= n ; ++ i) {
		sort(a + 1 , a + n + 1);
		int la = 1 , lb = 1;
		int rb = 0;
		for(int j = 1 ; i < n ; ++ j) {
			int s = 0;
			if(a[la] < b[lb]) {
				s += a[la];
				la ++;
			}
			else {
				s += b[lb];
				lb ++;
			}
			if(a[la] < b[lb]) {
				s += a[la];
				la ++;
			}
			else {
				s += b[lb];
				lb ++;
			}
			ans += s;
			b[++ rb] = s;
		}
	}
	cout << ans;
	return 0;
}