using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var accounts = new List<Account> { 

            new Account(1, "USD"),

            new Account(2, "CAD"),

            new Account(3, "GBP")

        };

        var currencies = new List<String> { "JPY", "USD", "CAD" };

        int accId = currencies

            .SelectMany(currency => accounts

                .Where(account => account.Currency.Equals(currency))

                    .Select(account => account.Id)).FirstOrDefault();

        Console.WriteLine(accId);

    }

    class Account

    {

        public Account (int id, string currency)

        {

            Id = id;

            Currency = currency;

        }

        public int Id { get; set; }

        public string Currency { get; set; }    

    }

}