import java.util.Scanner;
public class Arrays
{
 public static void clearScreen()
    {
      System.out.print('\u000C');
    }
 public static int equal (Integer a[], int b[])
{
    mergeSort(a);
    int i=0;
    int ans=-1;
    do
    {
        int target = b[i]+b[i+1];
        ans=binarySearch(a,target);
        i++;
        if(ans==1)
        return 1;
        else
        return -1;
    }
    while (ans=-1);

    return -1 ;
}
  public static int binarySearch (Integer []a, int target)
 {
    boolean found = false;
    int lo = 0;
    int hi = a.length-1;
    int mid = 0;
    while(lo<=hi&&!found)
    {
        mid=(lo+hi)/2;
        if(a[mid]==target)
            found=true;
        else
        {
            if(target>a[mid])
                lo=mid+1;
            else
                hi=mid-1;
        }
    }
    if(found)
        return 1;
    else
        return -1;
    }
    public static void mergeSort(Comparable [ ] a)
    {
        Comparable[] tmp = new Comparable[a.length];
        mergeSort(a, tmp,  0,  a.length - 1);
    }


    private static void mergeSort(Comparable [ ] a, Comparable [ ] tmp, int left, int right)
    {
        if( left < right )
        {
            int center = (left + right) / 2;
            mergeSort(a, tmp, left, center);
            mergeSort(a, tmp, center + 1, right);
            merge(a, tmp, left, center + 1, right);
        }
    }


    private static void merge(Comparable[ ] a, Comparable[ ] tmp, int left, int right, int rightEnd )
    {
        int leftEnd = right - 1;
        int k = left;
        int num = rightEnd - left + 1;

        while(left <= leftEnd && right <= rightEnd)
            if(a[left].compareTo(a[right]) <= 0)
                tmp[k++] = a[left++];
            else
                tmp[k++] = a[right++];

        while(left <= leftEnd)    // Copy rest of first half
            tmp[k++] = a[left++];

        while(right <= rightEnd)  // Copy rest of right half
            tmp[k++] = a[right++];

        // Copy tmp back
        for(int i = 0; i < num; i++, rightEnd--)
            a[rightEnd] = tmp[rightEnd];
    }

}