#include <cstdio>
#include <queue>
#include <algorithm>

using namespace std;

struct Edge
{
	int to, next, cp;
	int org;

	Edge(){};
	Edge(int _to, int _next, int _cp)
	{
		org = _cp;
		to = _to; next = _next; cp = _cp;
	}
};

const int MAXN = 1e2 + 5;
const int MAXK = 1e4 + 5;

int n;
int a[MAXN];
Edge e[MAXK];
int head[MAXN], br;
int source, target;

void add_edge(int v, int w, int cp)
{
	e[br++] = Edge(w, head[v], cp);
	head[v] = br++;
}

int sum;

void read_input()
{
	scanf("%d", &n);
	for(int i = 0; i < n; i++)
	{
		scanf("%d", &a[i]);
	}

	for(int i = 0; i < n + 2; i++)
	{
		head[i] = -1;
	}

	source = n;
	target = n + 1;

	for(int i = 0; i < n; i++)
	{
		for(int j = i + 1; j < n; j++)
		{
			if(a[i] > a[j])
			{
				sum++;
				add_edge(i, j, 1);
				add_edge(j, i, 0);
			}
		}
		add_edge(source, i, 1);
		add_edge(i, target, 0);
	}
}

int lvl[MAXN];

bool bfs(int v, int w)
{
	for(int i = 0; i <= target; i++)
	{
		lvl[i] = -1;
	}

	queue <int> q;
	q.push(v);
	lvl[v] = 0;

	while(!q.empty())
	{
		int tr = q.front(); q.pop();

		for(int z = head[tr]; z != -1; z = e[z].next)
		{
			int to = e[z].to;
			int cp = e[z].cp;

			if(cp > 0 && lvl[to] == -1)
			{
				lvl[to] = lvl[tr] + 1;
				q.push(to);
			}
		}
	}
	return lvl[w] != -1;
}

int pr[MAXN];

int dfs(int v, int flow)
{
	if(v == target)
	{
		return flow;
	}
	for(int z = pr[v]; z != -1; z = pr[v] = e[z].next)
	{
		int to = e[z].to;
		int cp = e[z].cp;

		if(cp > 0 && lvl[to] == lvl[v] + 1)
		{
			int aug_flow = dfs(to, min(flow, cp));
			if(aug_flow)
			{
				e[z].cp -= aug_flow;
				e[z ^ 1].cp += aug_flow;
				return aug_flow;
			}
		}
	}
	return 0;
}

int dinic(int fw)
{
	for(int i = 0; i < br; i++)
	{
		e[i].cp = e[i].org;
	}
	int ans = 0;
	while(bfs(source, target))
	{
		for(int i = 0; i <= target; i++)
		{
			pr[i] = head[i];
		}
		int delta = 0;
		do
		{
			delta = dfs(source, fw);
			ans += delta;
		}while(delta != 0);
	}
	return ans;
}

void solve()
{
	double ans = 0;
	for(int i = 1; i <= n; i++)
	{
		ans = max(ans, dinic(i) / n);
	}
	printf("%.6f\n", ans);
}

int main()
{
	read_input();
	solve();

	return 0;
}