def fibonacci_rec(n):
    if n==0:
        return 0
    elif n==1:
        return 1
    elif n>0 and n==int(n):
        return fibonacci_rec(n-1) + fibonacci_rec(n-2)
    else:
        return None

a=float(raw_input('n='))
print 'fibonacci_rec(n)is:',fibonacci_rec(a)
