AoC5.cs

using System;
using System.Linq;
using System.Collections.Generic;

public class Test
{
	public static int[] ReadInput(){
		string line;
		var elems = new List<int>();
		while ((line = System.Console.ReadLine()) != null)
	        {
	            elems.Add(int.Parse(line));
	        }
	    return elems.ToArray();
	}
	public static void Main()
	{
		var input = ReadInput();
		int pos = 0;
		int steps = 0;
		while(true){
			var new_pos = input[pos];
			if(new_pos >= 3){ //part 2
				input[pos]--;
			}else{
				input[pos]++;
			}
			pos += new_pos;
			
			steps++;
			if(pos < 0 || pos >= input.Length){
				System.Console.WriteLine(steps);
				return;	
			}
		}
	}
}