#include <iostream>
#include <string>

using namespace std;
string s;
string a = "BIMM";
string b = "BAMM";
string c = "BUMM";
int n, ok, i;
int main()
{
    cin >> n;
    getline(cin, s);
    ok = 0;
    for (i = 1; i <= n; ++i)
    {
        cin >> s;

        if (i % 3 == 0 && i % 5 == 0)
        {
            if (s[1] != c[1])
            {
                cout << i;
                ok = 1;
                break;
            }
        }
        else if (i % 3 == 0)
        {
            if (s[1] != a[1])
            {

                cout << i;
                ok = 1;
                break;

            }
        }
        else if (i % 5 == 0)
        {

            if (s[1] != b[1])
            {

                cout << i;
                ok = 1;
                break;
            }
        }

    }
    if (ok == 0)cout << "0";
    return 0;
}