Generating Triangle Problem

Hello, i have problem with generating meshes. I wanted to generate triangle but instead i have error. Well, just look at the code. Im not the expert but at first sight everything looks okay.

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class PolygonGenerator : MonoBehaviour {
 
     public List<Vector3> newVertices = new List<Vector3>();
     public List<int> newTriangles = new List<int>();
     public List<Vector2> newUV = new List<Vector2>();
 
     private Mesh mesh;
 
     // Use this for initialization
     void Start () {
         mesh = GetComponent<MeshFilter>().mesh;
 
         float x = transform.position.x;
         float y = transform.position.y;
         float z = transform.position.z;
 
         /*
         newVertices.Add(new Vector3(x, y, z));
         newVertices.Add(new Vector3(x+1, y, z));
         newVertices.Add(new Vector3(x+1, y-1, z));
         newVertices.Add(new Vector3(x, y-1, z));
 
         newTriangles.Add(0);
         newTriangles.Add(1);
         newTriangles.Add(3);
         newTriangles.Add(1);
         newTriangles.Add(2);
         newTriangles.Add(3);
         */
 
         newVertices.Add(new Vector3(x, y, z)); //0,0
         newVertices.Add(new Vector3(x+1, y, z)); //1,0
         newVertices.Add(new Vector3(x+1, y-1, z)); //1,-1
 
         newTriangles.Add(1);
         newTriangles.Add(2);
         newTriangles.Add(3);
 
 
         mesh.Clear();
         mesh.vertices = newVertices.ToArray();
         mesh.triangles = newTriangles.ToArray();
         mesh.Optimize();
         mesh.RecalculateNormals();
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 }