using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var input = new Tuple<int, int>[] {

            Tuple.Create(10, 300),

            Tuple.Create(20, 180),

            Tuple.Create(10, 120),

            Tuple.Create(30, 600)

        };

        var start = DateTimeOffset.Parse("2016-09-30T00:00:00Z");

Console.WriteLine("Expected");

        input.Zip(new[] {start}.Concat(input.Scan(start, (acc, source) => acc.AddSeconds(source.Item2))), (l, r) => Tuple.Create(l, r)).ForEach(x => Console.WriteLine(x));

Console.WriteLine("Actual");

        input.Publish(pub => pub.Zip(new[] {start}.Concat(pub.Scan(start, (acc, source) => acc.AddSeconds(source.Item2))), (l, r) => Tuple.Create(l, r))).ForEach(x => Console.WriteLine(x));

    }

}