include [HTML_REMOVED]

using namespace std;

const int N = 1e6 + 10;
int n;
int q[N];
int tmp[N];
typedef long long count ;

count merge_sort(int q[], int l, int r)
{
if(l >= r) return 0;

int mid = l + r >> 1;
count res = merge_sort(q, l, mid) + merge_sort(q, mid + 1, r);


int k = 0, i = l, j = mid + 1;  //i = l
while(i <= mid && j <= r)
{
    //进入双指针判断
    if(q[i] <= q[j]) tmp[k++] = q[i++];
    else 
    {
        tmp[k++] = q[j++];
        res += mid - i + 1;
    }
}
//这里mid已经+1 > i了
while(i <= mid) tmp[k++] = q[i++];
while(j <= r) {
    tmp[k++] = q[j++];

}


//将临时数组复制给q数组,要注意每次递归q数组的左值索引都是不同的，tmp为普通索引数组
for(int i = l, j = 0; i <= r; i++, j++) q[i] = tmp[j];

return res;

}

int main()
{
scanf(“%d”, &n);
for(int i = 0; i < n; i++) scanf(“%d”, &q[i]);

cout << merge_sort(q, 0, n-1) << endl;

return 0;

}