using System;
using System.Linq;

class ImeisvToImei
{
    static string Transform(string imeisv)
    {
        if (imeisv == null)
            throw new ArgumentNullException(nameof(imeisv));

        if (imeisv.Length != 16)
            throw new ArgumentOutOfRangeException(nameof(imeisv));

        var b = imeisv.Substring(0, 14);

        var sum = b
            .Select(ch => ch - '0')
            .Select((n, index) => (index % 2 == 0) ? n : n * 2)
            .Select(n => n / 10 + n % 10)
            .Sum();

        return $"{b}{10 - sum % 10}";
    }
}