#include #include #include #include #include //#include using namespace std; typedef long long ll; const int maxn = 1e6 + 10; int segment_tree[maxn]; void build(int node, int L, int R) { if(L == R) { segment_tree[node] = 0; } else { int mid = (L + R) / 2; build(2 * node, L, mid); build(2 * node + 1, mid + 1, R); segment_tree[node] = segment_tree[2 * node] + segment_tree[2 * node + 1]; } } int query(int node, int L, int R, int i, int j) { // L R i L R j L R if(i <= L and R <= j) { return segment_tree[node]; } if(R < i or j < L) { return 0; } int mid = (L + R) / 2; return query(2 * node, L, mid, i, j) + query(2 * node + 1, mid + 1, R, i, j); } void update(int node, int L, int R, int idx) { if(L == R) { segment_tree[node] += 1; return; } int mid = (L + R) / 2; if(idx <= mid) { update(2 * node, L, mid, idx); } else { update(2 * node + 1, mid + 1, R, idx); } segment_tree[node] = segment_tree[2 * node] + segment_tree[2 * node + 1]; } int main() { ios_base::sync_with_stdio(false); int n; cin >> n; vector v(n); vector > compressed; for(int i = 0; i < n; i++) { cin >> v[i]; compressed.push_back(make_pair(v[i], i)); } sort(compressed.begin(), compressed.end()); vector tmp; for(int i = 0; i < n; i++) { tmp.push_back(compressed[i].second); } reverse(tmp.begin(), tmp.end()); build(1, 0, n); vector smaller; for(int i = 0; i < n; i++) { update(1, 0, n, tmp[i]); smaller.push_back(query(1, 0, n, 0, tmp[i] - 1)); } build(1, 0, n); vector bigger; for(int i = n - 1; i >= 0; i--) { update(1, 0, n, tmp[i]); bigger.push_back(query(1, 0, n, tmp[i] + 1, n)); } reverse(bigger.begin(), bigger.end()); ll res = 0; for(int i = 0; i < n; i++) { res += bigger[i] * smaller[i]; } cout << res << endl; return 0; }