// NOTE: it is recommended to use this even if you don't understand the following code.

#include <fstream>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    // uncomment the following lines if you want to read/write from files
    // ifstream cin("input.txt");
    // ofstream cout("output.txt");
    int N;
    int t[10000];
    cin >> N;
    for (int i = 0; i < N; i++)
    {
        cin >> t[i];
        if (t[i] == 7)
        {
            cout << i + 1;
            return 0;
        }
    }
    cout << "-1";
    return 0;
}