Loop through for each key in Multi key dictionary

Question

I have written a code for adding multiple keys for a dictionary for that I defined my dictionary as follows and added the keys and values

Dictionary<int, Dictionary<int, List<int>>> outerDictionary = new Dictionary<int, Dictionary<int, List<int>>>();

Now I would like to loop through each keys in-order to get the required items can any one tell how can I loop through for each key value as per my dictionary

My code

protected void Page_Load(object sender, EventArgs e)

    {

        Dictionary<int, Dictionary<int, List<int>>> outerDictionary = new Dictionary<int, Dictionary<int, List<int>>>();

        Dictionary<int, List<int>> innerDictionary;

        ArrayList arrPayPeriodID = new ArrayList();

        ArrayList arrPayYear = new ArrayList();

        ArrayList arrEmpID = new ArrayList();

        int[] ipayYear = new int[] { };

        int[] iPayPeriodID = new int[] { };

        int[] iEmpID = new int[] { };

        int ipayYr = 2011;

        int ipayYr1 = 2011;

        int ipayYr2 = 2012;

        int ipayYr3 = 2012;

        int PayPeriodID = 1;

        int payperiodid1 = 2;

        int payperiodid2 = 2;

        int payperiodid3 = 2;

        int EmpID = 1;

        int EmpID1 = 1;

        int EmpID2 = 1;

        int EmpID3 = 1;

        arrEmpID.Add(EmpID);

        arrEmpID.Add(EmpID1);

        arrEmpID.Add(EmpID2);

        arrEmpID.Add(EmpID3);

        arrPayPeriodID.Add(PayPeriodID);

        arrPayPeriodID.Add(payperiodid2);

        arrPayPeriodID.Add(payperiodid3);

        arrPayPeriodID.Add(payperiodid1);

        arrPayYear.Add(ipayYr);

        arrPayYear.Add(ipayYr1);

        arrPayYear.Add(ipayYr2);

        arrPayYear.Add(ipayYr3);

        iEmpID = (int[])arrEmpID.ToArray(typeof(int));

        iPayPeriodID = (int[])arrPayPeriodID.ToArray(typeof(int));

        ipayYear = (int[])arrPayYear.ToArray(typeof(int));

        DataTable table = GetTable(iEmpID, ipayYear, iPayPeriodID);

        DataRow row = table.Rows[0];

        for (int i = 0; i < table.Rows.Count; i++)

        {

            DataRow row1 = table.Rows[i];

            var employeeId = (int)row1["EmpID"];

            var payYear = (int)row1["Year"];

            var payId = (int)row1["PayID"];

            

            if (!outerDictionary.TryGetValue(employeeId, out innerDictionary))

            {

                innerDictionary = new Dictionary<int, List<int>>();

                outerDictionary.Add(employeeId, innerDictionary);

            }

            List<int> list;

            if (!innerDictionary.TryGetValue(payYear, out list))

            {

                list = new List<int>();

                innerDictionary.Add(payYear, list);

            }

            list.Add(payId);

        }

    }

    static DataTable GetTable(int[] empID, int[] payYr, int[] payID)

    {

        // Here we create a DataTable with four columns.

        DataTable table = new DataTable();

        table.Columns.Add("EmpID", typeof(int));

        table.Columns.Add("Year", typeof(int));

        table.Columns.Add("PayID", typeof(int));

        // Here we add five DataRows.

        for (int i = 0; i < empID.Length; i++)

        {

            table.Rows.Add(empID[i], payYr[i], payID[i]);

        }

        return table;

    }