#include <iostream>
#include <sstream>
#include <cstdlib>
using namespace std;
void sherry()
{
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
int main()
{
    sherry();
    long long x, a, flag = 1;
    cin >> x;
    long long arr[x];
    for (int i = 0; i < x; i++)
    {
        cin >> arr[i];
    }
    cin >> a;
    for (int j = 0; j < x; j++)
    {
        if ((arr[j] == a) && (flag == 1))
        {
            cout << j;
            flag = 0;
        }
    }
    if (flag)
    {
        cout << "-1";
    }
}