#include <iostream>
using namespace std;

int longestDist(const int arr[], const int arrSize) {
    int first_index, second_index, difference, result = 0;
    if (arrSize < 2) {
        return -2;
    }
    else {
        for (int i = 0; i < arrSize - 1; ++i) {
            int temp = arr[i];
            first_index = i;

            for (int j = i + 1; j < arrSize; ++j) {

                if (temp == arr[j]) {
                    second_index = j;
                    difference = second_index - first_index;

                if (difference > 0) {
                        result = first_index;
                        return result;
                    }
                }
            }
        } return -1;
    }
}

int main() {
    int sizeArray;
    cin >> sizeArray;
    int arr[100];
    for (int i = 0; i < sizeArray; ++i) {
        cin >> arr[i];
    }
    cout << longestDist(arr, sizeArray);
}