Problem:
Score: 400 points

Problem Statement

The Kingdom of Takahashi has N towns, numbered 1 through N.

There is one teleporter in each town. The teleporter in Town i (1 \leq i \leq N) sends you to Town A_i.

Takahashi, the king, loves the positive integer K. The selfish king wonders what town he will be in if he starts at Town 1 and uses a teleporter exactly K times from there.

Help the king by writing a program that answers this question.

Constraints

2 \leq N \leq 2 \times 10^5

1 \leq A_i \leq N

1 \leq K \leq 10^{18}

Input

Input is given from Standard Input in the following format:

N K
A_1 A_2 \dots A_N

Output

Print the integer representing the town the king will be in if he starts at Town 1 and uses a teleporter exactly K times from there.

Sample Input 1

4 5
3 2 4 1

Sample Output 1

4

If we start at Town 1 and use the teleporter 5 times, our travel will be as follows: 1 \to 3 \to 4 \to 1 \to 3 \to 4.

Sample Input 2

6 727202214173249351
6 5 2 5 3 2

Sample Output 2

2

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
namespace program{
    public class ABC167{
        public static void Main(string[] args){
            var input = Console.ReadLine().Split();
            var N = long.Parse(input[0]);
            var K = long.Parse(input[1]);
            var A = Console.ReadLine().Split().Select(a => long.Parse(a)).ToArray();
            long before = 0;
            long[] loop = new long[N + 1];
            loop[0] = 1;
            var visited = new bool[N];
            visited[0] = true;
            //ループを見つける
            long position = 0;
            var i = 1;
            for(i = 1; i < N + 1; i++){
                if(visited[A[position]-1]){
                    before = Array.IndexOf(loop, A[position]);
                    break;
                }else{
                    loop[i] = A[position];
                    visited[A[position]-1] = true;
                    position = A[position] - 1;
                }
            }
            
            if(K <= before){
                Console.WriteLine(loop[(int)K]);
            }else{
                var j = (int)((K-before) % (i - before));
                Console.WriteLine(loop[j+(int)before]);
            }
        }
    }
}