import matplotlib.pyplot as plt

def f(n):
    if n==0:
        return 1
    elif n==1:
        return 2
    elif n>=2:
        return 1+f(n-1)-.5*f(n-2)

for a in range(30):
    print(f(a))
    plt.plot(a,f(a),'o-')

plt.show()