Invalid token '=' in class, struct, or interface member declaration c#

this may be a simple question for people, but I can't see why this is occurring. here is my code 1st:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace GameCore
{
    public class PlayerCharacter
    {

        public void Hit(int damage)
        {
            Health -= damage;

            if (Health <= 0)
            {
                IsDead = true;
            }
        }

        public int Health { get; private set; } = 100;
        public bool IsDead{ get; private set; }

    }
}

now Visual studio is giving the Invalid token error on the assignment sign (=) (as per the title), and I can not see why. can anyone shed light on this please?

What I'm trying to do is set the int of Health to 100, and each time a character takes damage, then Health is decreased. Thanks all.

I'm using Visual Studio 2013 v12.0.40629.00 update 5