// we have defined the necessary header files here for this problem.
// If additional header files are needed in your program, please import here.

int main()
{
    int A[55] = {0};
    int N;
    A[1] = 1;
    A[2] = 1;
    A[3] = 2;
    for(int i = 4;i<51;i++)
    {
        A[i] = A[i-1]+A[i-3];
    }
    while(scanf("%d",&N)!=EOF)
    {
        printf("%d\n",A[N]);
    }
    // please define the C input here. For example: int n; scanf("%d",&n);
    // please finish the function body here. 
    // please define the C output here. For example: printf("%d\n",a);    
    return 0;
}