#include <bits/stdc++.h>

using namespace std;

int main(){
	int n;
        
	while(cin >> n){
            vector<long long> nums(n, 0);
                        
            for (int i = 0; i < n; ++i) {
                cin >> nums[i];
            }
            
            if (n == 1 || n == 2) {
                cout << 1 << endl;
                continue;
            }
            
            reverse(nums.begin(), nums.end());
            
            long long dt = nums[1] - nums[0];
            
            int i = 2;
            for (; i < n; ++i) {
                long long new_dt = nums[i] - nums[i-1];
                if (new_dt != dt)
                    break;
            }
            
            cout << (n-i + 1) << endl;
	}
}