#include <stdio.h>

int main() {
    int n, a[20] = {0, 1, 1};
    scanf("%d", &n);
    for (int i = 3; i < n; ++i) {
        a[i] = a[i - 3] + 2 * a[i - 2] + a[i - 1];
    }
    printf("%d\n", a[n - 1]);
    return 0;
}