#include <bits/stdc++.h> #define ll long long using namespace std; struct node { ll data; ll num; } f[5000001]; ll n, c[5000001], ans, a[5000001]; bool cmp(node a, node b) { if (a.data == b.data) { return a.num < b.num; } return a.data < b.data; } inline ll lowbit(ll i) { return i & (-i); } inline ll sum(ll x) { ll s = 0; for (; x > 0; x -= lowbit(x)) { s += c[x]; } return s; } int main() { cin >> n; for (ll i = 1; i <= n; i++) { cin >> f[i].data; f[i].num = i; } sort(f + 1, f + 1 + n, cmp); for (int i = 1; i <= n; i++) { a[f[i].num] = i; } for (ll i = n; i > 0; i--) { ans += sum(a[i]); for (ll j = a[i]; j <= n; j += lowbit(j)) { c[j]++; } } cout << ans; return 0; }