#include <bits/stdc++.h>
using namespace std;

int main() {
    static const int maxn = 1000010;
    static int n;
    scanf("%d", &n);
    static int a[maxn], r[maxn];
    static vector<int> vec[maxn];
    for (int i = 1; i <= n; i++) scanf("%d", a + i), r[a[i]] = i;
    for (int i = 1; i <= n - 2; i++) vec[min(r[i], r[i + 1])].push_back(i + 2);
    struct BIT {
        int a[maxn];
        inline void insert(const int p) {
            for (int i = p; i; i -= i & -i) a[i]++;
            return;
        }
        inline int query(const int p) {
            int ret = 0;
            for (int i = p; i <= n; i += i & -i) ret += a[i];
            return ret;
        }
    };
    static BIT t;
    int ans = (n * (n - 1) >> 1) + (n << 1) - (r[1] - 1);
    for (int i = 1; i <= n; i++) {
        for (int p : vec[i]) ans -= t.query(p);
        t.insert(a[i]);
    }
    printf("%d.%d\n", ans >> 1, (ans & 1) * 5);
    return 0;
}