Get Input struct data from displacement function

I'm just beginning with surface shaders and I'm trying to figure out how to acces Input struct from the displacement function "disp", within the surf function I can just type IN. to acces any input struct I want (UV), but from disp function wich is the function that manage the displacement, I cant. Can some one help me to figure out how to do that? Thanks!
Edit: I would like to use this function tex2D (_MainTex, IN.uv_MainTex) inside disp function is it possible?

Code (CSharp):

1. Shader "Planet Generator/Test" {
2.         Properties {
3.             _Color ("Color", color) = (1,1,1,0)
4.             _MainTex ("Base (RGB)", 2D) = "white" {}
5.             _DispTex ("Disp Texture", 2D) = "gray" {}
6.             _Displacement ("Displacement", Range(0, 1.0)) = 0.3
7.             _Tess ("Tessellation", Range(1,32)) = 4
8.         }
9.         SubShader {
10.             Tags { "RenderType"="Opaque" }
11.             LOD 300
12.          
13.             CGPROGRAM
14.             #pragma surface surf Lambert vertex:disp tessellate:tessDistance
15.             #pragma target 4.6
16.             #include "Tessellation.cginc"
17.  
18.             struct appdata {
19.                 float4 vertex : POSITION;
20.                 float4 tangent : TANGENT;
21.                 float3 normal : NORMAL;
22.                 float2 texcoord : TEXCOORD0;
23.             };
24.  
25.             float _Tess;
26.  
27.             float4 tessDistance (appdata v0, appdata v1, appdata v2) {
28.                 float minDist = 5.0;
29.                 float maxDist = 5.0;
30.                 return UnityDistanceBasedTess(v0.vertex, v1.vertex, v2.vertex, minDist, maxDist, _Tess);
31.             }
32.  
33.             sampler2D _DispTex;
34.             float _Displacement;
35.  
36.             void disp (inout appdata v)
37.             {
38.                 float d = tex2Dlod(_DispTex, float4(v.texcoord.xy,0,0)).r * _Displacement;
39.                 v.vertex.xyz += v.normal * d;
40.             }
41.  
42.             struct Input {
43.                 float2 uv_MainTex;
44.             };
45.  
46.             sampler2D _MainTex;
47.             fixed4 _Color;
48.  
49.             void surf (Input IN, inout SurfaceOutput o) {
50.                 half4 c = tex2D (_MainTex, IN.uv_MainTex) * _Color;
51.                 o.Albedo = c.rgb;
52.             }
53.             ENDCG
54.         }
55.         FallBack "Diffuse"
56.     }