One-line Calculator in C#

using System;
namespace Calculator
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine("Enter an equation like this 25+78 then press ENTER\n");
            int x , y , i=0 , n , digits , max;
            string input , num1="" , num2="";
            char op;
            input=Convert.ToString(Console.ReadLine());
            digits=input.Length-1;
            again:
            i=i+1;
            if(input[i]=='+'||input[i]=='-'||input[i]=='*'||input[i]=='/')
            {
                op=input[i];
                n=i;
                while(n>0)
                {
                num1=num1+input[i-n];
                n=n-1;
            }
            digits=digits-num1.Length;
            max=digits;
            while(digits>0)
            {
                num2=num2+input[i+1+(max-digits)];
                digits=digits-1;
            }
        }
        else
        {
            goto again;
        }
        x=Convert.ToInt32(num1);
        y=Convert.ToInt32(num2);
        Console.Write(" = ");
        if(op=='+')
        {
            Console.WriteLine(x+y);
        }
        else if(op=='-')
        {
            Console.WriteLine(x-y);
        }
        else if(op=='*')
        {
            Console.WriteLine(x*y);
        }
        else if(op=='/')
        {
            Console.WriteLine(x/y);
        }
        }
    }
}