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

public class Amusement {

    public static void main(String[] args) {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String s;
        try {
            while ((s = br.readLine()) != null && !s.isEmpty()) {
                int n = Integer.parseInt(s);
                String[] seq = br.readLine().split(" ");

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

                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);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}