int viralAdvertising(int n) {
    stack<int> st;
    st.push(0);
    int tmp = 5;
    int t = 0;
    for (int i = 1; i <= n; i++) {
        t = floor(tmp / 2) + st.top();
        tmp = floor(tmp / 2) * 3;
        st.push(t);
    }

    return t;
}