File not found Visual Studio 2015 Exception

I get file not found error even though I have the required file inside the project directory. No compilation errors.

Here is my startup.cs class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Configuration;

namespace OdeToFood
{
public class Startup
{
    public Startup()
    {
        var builder = new ConfigurationBuilder()
             .AddJsonFile("config.json");
        Configuration = builder.Build();
    }

    public IConfiguration Configuration { get; set; }

    // This method gets called by the runtime. Use this method to add services to the container.
    // For more information on how to configure your application, visit http://go.microsoft.com/fwlink/?LinkID=398940
    public void ConfigureServices(IServiceCollection services)
    {
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.Run(async (context) =>
        {
            var message = Configuration["greeting"];
            await context.Response.WriteAsync(message);
        });
    }
}
}

      

        
        
        
      

    

And this is the error message I get when I create it.

System.IO.FileNotFoundException: The configuration file 'config.json' was not found and is not optional.
   at Microsoft.Extensions.Configuration.FileConfigurationProvider.Load(Boolean reload)
   at Microsoft.Extensions.Configuration.ConfigurationRoot..ctor(IList`1 providers)
   at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()
   at OdeToFood.Startup..ctor()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.Extensions.Internal.ActivatorUtilities.ConstructorMatcher.CreateInstance(IServiceProvider provider)
   at Microsoft.AspNetCore.Hosting.Internal.StartupLoader.LoadMethods(IServiceProvider services, Type startupType, String environmentName)
   at Microsoft.AspNetCore.Hosting.WebHostBuilderExtensions.<>c__DisplayClass1_0.b__1(IServiceProvider sp)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.ScopedCallSite.Invoke(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureStartup()
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices()
   at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

      

        
        
        
      

    

Screenshot of file image

How do I fix this?

thank