bool match_back(std::vector<int>& state, int v)
{
    return state.size() >= 2
            && state[state.size() - 1] == v
            && state[state.size() - 2] == v;
}

int erase_back(std::vector<int>& state, int v)
{
    int erased = 0;
    while (state.size() > 0 && state[state.size() - 1] == v) {
        state.pop_back();
        erased++;
    }
    return erased;
}


int main()
{
    //std::istringstream is ("5 1 3 3 3 2");
    std::istringstream is ("10 3 3 2 1 1 1 2 2 3 3");
    int erased = 0;
    std::vector<int> state;
    int erase_v = -1;
    int v;
    while (is >> v) {
        if (erase_v == v) {
            erased++;
        }
        else if (match_back(state, v)) {
            erased += erase_back(state, v);
            erase_v = v;
            erased++;
        }
        else {
            erase_v = -1;
            state.push_back(v);
        }
    }
    cout << erased << endl;
    return 0;
}