//uva580 #include<iostream> using namespace std; int main(){ int n; while (cin >> n && n){ int U[31] = {0}, L[31] = {0}; U[3] = 1; for(int i = 4 ; i <= n ; i++){ U[i] = L[i-1] + (U[i-1] - L[i-3] + (1<<(i-4))); L[i] = U[i-1] + L[i-1]; } cout << U[n] + L[n] << "\n"; } }