Two Textures one plane

Shader "Custom/TwoSided" {
    Properties {
        _FirstTex ("First (RGB)", 2D) = "white" {}
        _SecondTex ("Second (RGB)", 2D) = "white"{}
    }

    SubShader {

    Pass {
      Cull Off
      CGPROGRAM
      #pragma vertex vert
      #pragma fragment frag
      #include "UnityCG.cginc"


        sampler2D _FirstTex;
        sampler2D _SecondTex;

      struct v2f {
          float4 pos : SV_POSITION;
          fixed4 color : COLOR;
          float4 tex : TEXCOORD0;
      };

      v2f vert (appdata_base v)
      {
          v2f o;

          o.pos = mul (UNITY_MATRIX_MVP, v.vertex);

          float3 viewVector = normalize(_WorldSpaceCameraPos);

          //Converting the normal to world space as we have view vector in world space. We need to transfer both to same space for any operations.
          float3 worldSpaceNormal = normalize(mul((float3x3)_World2Object,v.normal));

          //Dot product to know which side we are facing
          float NdotL = dot(viewVector,v.normal);

          o.color.w = NdotL;

          o.tex = v.texcoord;

          return o;
      }

      fixed4 frag (v2f i) : COLOR0 {
          if(i.color.w > 0.0f)
          {
            i.color.xyz = tex2D(_FirstTex, float2(i.tex)).xyz;
          }
          else
          {
            i.color.xyz = tex2D(_SecondTex, float2(i.tex)).xyz;
          }

          return i.color;
      }
      ENDCG
    }
  }
}