#include <iostream>

using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    while(true)
    {
        int N;
        cin>>N;
        if(cin.good()==false)
        {
            break;
        }

        int * arr = new int[N];
        for(int i=0;i<N;i++)
        {
            cin>>arr[i];
        }

        int result=2;

        if(N<3)
        {
            cout<<1<<endl;
            continue;
        }
        int dif=arr[N-1]-arr[N-2];

        bool printed=false;
        for(int i=N-3;i>=0;i--)
        {
            //cout<<"fc"<<endl;
            if(arr[i]+dif==arr[i+1])
            {
                result++;
            }
            else
            {
                cout<<N-result+1<<endl;
                printed=true;
                break;
            }
        }
        if(printed==false)
        {
            cout<<N-result+1<<endl;
        }
    }
    return 0;
}