文件目录

#include <bits/stdc++.h>
using namespace std;
int n, a[100005], t[100005];
long long ans = 0;
void gb_sort(int l, int r)
{
    if (l >= r)
        return;
    int mid = l + r >> 1;
    gb_sort(l, mid);
    gb_sort(mid + 1, r);
    int i = l, nl = l, ml = mid + 1;
    while (nl <= mid && ml <= r)
        if (a[nl] > a[ml])
        {
            ans += mid - nl + 1;
            t[i++] = a[ml++];
        }
        else
            t[i++] = a[nl++];
    while (nl <= mid)
        t[i++] = a[nl++];
    while (ml <= r)
        t[i++] = a[ml++];
    for (i = l; i <= r; i++)
        a[i] = t[i];
}
int main()
{
    cin >> n;
    for (int i = 1; i <= n; i++)
        scanf("%d", a + i);
    gb_sort(1, n);
    cout << ans;
    return 0;
}