ol_4_15

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    ifstream cin("input.txt");

    short n;
    cin>>n;

    bool no = true;
    string pre = "", pre2 = "";
    for(int i = 0; i < n; i++)
    {
        string cur;
        cin>>cur;
        if (pre2 == cur)
        {
            if (no)
                no = false;
            cout<<i<<' ';
        }
        pre2 = pre;
        pre = cur;
    }
    if (no)
        cout<<-1;
}