func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxn = 111111;   long long tree[maxn * 4];   void Insert(int o, int l, int r, int k, int v) {     if (l == r) {       tree[o] = v;       return;     }     int mid = (l + r) >> 1;     if (k <= mid)       Insert(o * 2, l, mid, k, v);     else       Insert(o * 2 + 1, mid + 1, r, k, v);     tree[o] = tree[o * 2] + tree[o * 2 + 1];   }   long long Query(int o, int l, int r, int L, int R) {     if (L <= l && r <= R) return tree[o];     int mid = (l + r) >> 1;     long double ans = 0;     if (L <= mid) ans += Query(o * 2, l, mid, L, R);     if (R > mid) ans += Query(o * 2 + 1, mid + 1, r, L, R);     return ans;   }   int n, x, a[maxn], f[maxn];   int main() {     cin >> n;     long double ans = 0;     for (int i = 1; i <= n; i++) cin >> a[i], f[a[i]] = i;     for (int i = 1; i <= n; i++) {       ans += Query(1, 1, n, a[i], n);       Insert(1, 1, n, a[i], 1);     }     ans *= ((long long)n * (n + 1));     memset(tree, 0, sizeof(tree));     long long last = 0;     for (int i = 1; i <= n; i++) {       ans -= (last + Query(1, 1, n, a[i], n));       last = last + Query(1, 1, n, a[i], n);       Insert(1, 1, n, a[i], f[a[i]] * 2);     }     for (int i = 1; i <= n; i++)       ans += ((long long)(n - i + 1) * i * (i - 1) / 2);     ans /= ((long long)n * (n + 1));     cout << setprecision(15) << ans << endl;   }   