using System;

public class Program

{

    public static void Main()

    {

        int d,z,diff=1000,x=0,y=0,i,j;

        int [] a= new int[5];

        for(i=0;i<4;i++)

        {

            a[i]=Convert.ToInt32(Console.ReadLine());

        }

        for(i=0;i<4;i++)

        {

            for(j=0;j<4;j++)

            {

                if(i!=j)

                {

                    d=a[i]-a[j];

                    z=Math.Abs(d);

                    while(diff>z)

                    {

                        diff=z;

                        x=i;

                        y=j;

                    }

                }

            }

        }

        Console.WriteLine("{0}{1}",a[x],a[y]);

    }

}