#include
#include
#include
#include
#include
#include
#include
#include
using namespace std;
typedef long long LL;
#define MAXN 30
LL mm[MAXN + 1][2][2][2];
LL dp(int left, int late, int a, int b) {
LL& ret = mm[left][late][a][b];
if (ret != -1) return ret;
if (left == 0) return ret = 1;
ret = 0;
if (late == 0) ret += dp(left - 1, 1, b, 0);
if (a + b <= 1) ret += dp(left - 1, late, b, 1);
ret += dp(left - 1, late, b, 0);
return ret;
}
void run() {
memset(mm, -1, sizeof(mm));
cout << dp(MAXN, 0, 0, 0) << endl;
}
int main() {
run();
}