import java.util.Scanner;

/*
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 */

/**
 *
 * @author cteam037
 */
public class Amusement {
    
    
    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()) {
           
            int n = sc.nextInt();
            int rozdil = 0;
            int predchozi = -1;
            int index = 1;
            for(int i = 0; i <n; i++) {
                
                int a = sc.nextInt();
                if(predchozi == -1) {
                    predchozi = a;
                    continue;
                }
                
                if(i == 1) {
                    rozdil = predchozi - a;
                    predchozi = a;
                    continue;
                }
                
                int rozdilTed = predchozi - a;
                
                if(rozdil == rozdilTed) {
                    predchozi = a;
            
                } else {
                    rozdil = rozdilTed;
                    index = i;
                    predchozi = a;
                }              
            }
            
            System.out.println(index);
            
        }
    }
}