using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using Debug = System.Diagnostics.Debug;
using StringBuilder = System.Text.StringBuilder;
public class SuccessfulMerger
{
    public int minimumMergers(int[] road)
    {
        var n = road.Length;
        var G = Enumerate(n, x => new List<int>());
        for (int i = 0; i < n; i++)
        {
            G[i].Add(road[i]);
            G[road[i]].Add(i);
        }
        var isCycle = new bool[n];
 
        //閉路検出
        {
            for (int i = 0; i < n; i++)
                isCycle[i] = true;
            var notCycle = Graph.TopologicalSort(G);
            foreach (var x in notCycle)
                isCycle[x] = false;
        }
    }
     static public T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
}
 
#region TopologicalSort
static partial class Graph
{
    //順序をいじりたい場合はQueueから変える
    //使わない奴がある場合はcountのその位置に予め-1を入れて渡す
    //循環してるとサイズが小さくなるはず？
    static public int[] TopologicalSort(List<int>[] G, int[] count = null)
    {
        const int Capacity = 1;//有向ならば0無向ならば1
        var n = G.Length;
        if (count == null)
        {
            count = new int[n];
            foreach (var l in G)
                foreach (var x in l) count[x]++;
        }
        var ret = new List<int>();
        var q = new Queue<int>();
        for (int i = 0; i < n; i++)
            if (count[i] == Capacity) q.Enqueue(i);
        while (q.Any())
        {
            var p = q.Dequeue();
            ret.Add(p);
            foreach (var x in G[p])
                if (--count[x] == Capacity) q.Enqueue(x);
        }
        return ret.ToArray();
    }
 
}
#endregion

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