using System;

using System.Linq;

public class Program

{

    public static void Main()

    {   

        var upc = "03760016095";

        CheckDigit(upc).Dump();

    }

    private static int CheckDigit(string upc) 

    {

        var digit = upc

            .Take(11)

            .Select((d, i) => new { digit = int.Parse(d.ToString()), isOddPosition = i % 2 == 0 })

            .Sum(a => a.digit * (a.isOddPosition ? 3 : 1)) % 10;

        return (10 - digit) % 10;

    }

}