#include<iostream> using namespace std; long long solve(int n) { long long a[51] = { 0, 3, 6, 6 }; if (n < 4) return a[n]; for (int i = 4; i <= n; ++i) { a[i] = a[i - 1] + 2 * a[i - 2]; } return a[n]; } int main() { int n; while (cin >> n) { cout << solve(n) << endl; } return 0; } |
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