include

using namespace std;

int n; long long f[66];

int main() {

f[1] = 1, f[2] = 2, f[3] = 3;
for (int i = 4; i <= 60; i++) {
    f[i] = f[i - 1] + f[i - 3];
}

int x;
while (cin >> x) {
    cout << f[x] << endl;
}
return 0;

}