a=[0 for i in range(100)]
a[0]=1
a[1]=2
a[2]=4
for i in range(3,99):
    a[i]=a[i-1]+a[i-2]+a[i-3]
while 1:
    n=int(input())
    if n==0:
        break
    else:
        print(a[n-1])