import com.sun.org.apache.xerces.internal.impl.dv.xs.IntegerDV;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.InputStreamReader;

public class Amusement {

    public static void main(String... args) throws Exception {
       // try (BufferedReader reader = new BufferedReader(new FileReader(new File("t1.in")))) {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {

            String line;
            while ((line = reader.readLine()) != null) {
                int len = Integer.parseInt(line);

                String nums[] = reader.readLine().split(" ");

                int index = len;

                int rozdil = 0;
                int last = 0;
                int pom = 0;

                if (len > 1) {
                    last = Integer.parseInt(nums[len - 2]);
                    rozdil = Integer.parseInt(nums[len - 1]) - last;
                    index--;
                }

                for (int i = len - 3; i >= 0; i--) {
                    pom = Integer.parseInt(nums[i]);
                    if (last - pom == rozdil) {
                        index--;
                    } else {
                        break;
                    }
                    last = pom;
                }

                System.out.println(index);
            }
        }
    }

}