int numRocks, allRocks = 0xfffffff;
cin >> numRocks;
while (numRocks--) {
    string s;
    cin >> s;
    int thisRock = 0;
    for (char ch : s)
        thisRock |= 1 << (ch - 'a');
    allRocks &= thisRock;
}
cout << __builtin_popcount(allRocks) << endl;
return 0;