虽然是自己写出来的，还是有点不理解，最后的最大值为什么要除以二

#include <bits/stdc++.h>
#define maxn 1010
using namespace std;
long long f[maxn][maxn];
//int head[maxn];
int a[maxn];
//int tail[maxn];
int n;
int tmp;
long long ma = 0;

int main() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> tmp;
		a[i] = tmp;
		a[i + n] = tmp; //断环成链
	}

	for (int len = 2; len <= 2 * n; len++) { //枚举区间长度
		for (int i = 1; i <= 2 * n - len + 1; i++) { //枚举起始点
			int j = i + len - 1; //设定终点
			for (int k = i; k < j; k++) { //枚举断点
				f[i][j] = max(f[i][j], f[i][k] + f[k + 1][j] + (a[j + 1] * a[k + 1] *
				              a[i])); //j+1是因为j所需的尾标记是j+1的头标记，k+1同理，
				ma = max(ma, f[i][j]);
			}
		}
	}
	cout << ma / 2;
	return 0;
}