error CS1001: Unexpected symbol `{', expecting identifier need help :(

Please use code tags.

using UnityEngine;
using UnityEngine.PostProcessing;

namespace UnityEditor.PostProcessing. {
    [CustomPropertyDrawer(typeof(UnityEngine.PostProcessing.MinAttribute))]
    sealed class MinDrawer : PropertyDrawer {

        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label) {

            UnityEngine.PostProcessing.MinAttribute attribute = (UnityEngine.PostProcessing.MinAttribute)base.attribute;


            if(property.propertyType == SerializedPropertyType.Integer) {
                int v = EditorGUI.IntField(position, label, property.intValue);
                property.intValue = (int)Mathf.Max(v, attribute.min);
            }
            else if(property.propertyType == SerializedPropertyType.Float) {
                float v = EditorGUI.FloatField(position, label, property.floatValue);
                property.floatValue = Mathf.Max(v, attribute.min);
            }
            else {
                EditorGUI.LabelField(position, label.text, "Use Min with float or int.");
            }
        }
    }
}

Remove the period at the end your namespace:
namespace UnityEditor.PostProcessing.