Convert.ToInt64();

Convert.ToInt64(); Method in C#
This strategy is utilized to converts the specified data type to an equivalent 64-bit signed integer. 
So let's see the example which demonstrates Convert.ToInt64();method as shown below.
Program
using System;

namespace ToInt64_program
{
    class program
    {
        static void Main(string[] args)
        {
          double f=123456789012345678.555;

            /* converting double to specified int */
           long value = Convert.ToInt64(f);

            /* Display the converted float value */
            Console.Write("float value= "+f+"\nConverted to Int_64_bit={0} ", value,f); 
            Console.ReadKey();
        }
    }
}

 Output