#include <bits/stdc++.h>
using namespace std;

#define PB push_back
#define CL(A, I) (memset(A, I, sizeof(A)))
#define D(X) cout<<"  "<<#X": "<<X<<endl;
#define FOR(i, m, n) for(int i(m); i < n; i++)
#define F(n) FOR(i, 0, n)
#define FF(n) FOR(j, 0, n)
#define aa first
#define bb second

typedef long long ll;
typedef vector<ll> vi;
typedef pair<ll, ll> ii;
typedef vector<ii> vii;

ll arr[1005];
int main() {
ll N;
	while(cin>>N){
		F(N){
			cin>>arr[i];
		}
		ll maxlen=1;
		ll maxf=N-1;
		for(int j=1;j<=1;j++){
			ll diff=arr[N-1]-arr[N-1-j];
			ll k=N-1;
			ll len=1;
			while(k-j>=0 && arr[k]-arr[k-j]==diff){
				len++;
				k--;
			}
			if(maxlen<len){
				maxlen=len;
				maxf=k;
			}
		}
		cout<<maxf+1<<endl;	
	}
	
}