using System;
					
public class Program
{
	public static void Main()
	{
		int[] A = {-7, 1, 5, 2, -4, 3, 0};
		
		int length = A.Length;
		
		
		
		
		if(length < 3)
		{
			System.Console.Write("-1");
		}
		else
		{
            for(int k=1; k<length; k++)
            {
				int sum1=0, sum2=0;
                for(int i=0; i<k; i++)
                {
                    sum1=sum1+A[i];
                
                }
                for(int j=k+1; j<length; j++)
                {
                    sum2=sum2+A[j];
                }
                if(sum1 == sum2)
                {
                    System.Console.Write(k);
                    break;
                }
                if(k==length)
                {
                    System.Console.Write("-1");
                }
		    }
        }
		
	}
}