/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/* 
 * File:   main.cpp
 * Author: cteam007
 *
 * Created on October 28, 2017, 9:06 AM
 */

#include <bits/stdc++.h>

#define ll long long int

using namespace std;

ll arr[1002];
ll diff;
int ind;
int n;
/*
 * 
 */
int main() {
    ll a;
    while(cin>>n){
        memset(arr,0,sizeof(arr));
        for(int i=0;i<n;i++){
            cin>>a;
            arr[i] = a;
        }
        if(n==1){
            cout << "1" << endl;
            continue;
        }
        for(int i=n-1;i>=1;i--){
            if(i==n-1){
               diff = arr[i] - arr[i-1]; 
//               cout << diff << ":" << endl;
               ind = i-1;
            }
            else{
//                cout << arr[i]  << " " << arr[i-1] << " ";
                if(arr[i] - arr[i-1] != diff){
                    ind = i;
                    break;
                }
                else{
                    ind = i-1;
                }
            }
        }
        cout << (ind+1) <<  endl;
    }
    

    return 0;
}