/*
 * 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: cteam025
 *
 * Created on October 28, 2017, 9:12 AM
 */

#include <cstdlib>
#include <locale>
#include <iostream>

#define MAX(a,b) ((a)>(b)?(a):(b))
using namespace std;

/*
 * 
 */
int main(int argc, char** argv) {
    
    ios::sync_with_stdio(false);
    
    
    while(cin.good()){
        int numCnt;
        
        cin >> numCnt;
        
        if (!cin.good())
            return 0;
        
        
        int actDiff, seqCnt, seqCntMax;
        int prevNum;
        
        
        actDiff = seqCntMax = 0;
        seqCnt = 1;
        cin >> prevNum;
        int lastStart = 0;
        for(int i=1; i<numCnt; ++i){
            int num;
            cin >> num;
            
            if (num-prevNum != actDiff){
                seqCntMax = MAX(seqCntMax, seqCnt);
                seqCnt = 1;
                actDiff = num-prevNum;
                lastStart = i-1;
            }else{
                ++seqCnt;
            }
        
            prevNum = num;
        }
        
        cout << lastStart+1 << endl;
    
    
    
    }
    
    
    return 0;
}