import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Random;

public class Amusement {

    public static void main(String[] args) {

        while (true) {
            int[] arr = null;

            try {
                BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
                String s = br.readLine();
                if ((s == null)||s.isEmpty()) break;

                int n = Integer.parseInt(s);
                String[] seq = br.readLine().split(" ");

                arr = new int[n];
                for (int i =0; i < n; i++) arr[i] = Integer.parseInt(seq[i]);

            } catch (IOException e) {
                break;
            }

            if (arr.length == 1) {
                System.out.println("1");
            } else {
                int index = arr.length - 2;
                int dif = arr[arr.length-1] - arr[arr.length - 2];
                for (int i = arr.length - 2; i > 0; i--) {
                    if ((arr[i] - dif) == arr[i-1]) {
                        index--;
                    } else {
                        break;
                    }
                }
                System.out.println(index+1);
            }
        }



    }

}