def fb(n):

if n ==1: return 1

n1, n2 = 0, 1 #f(1)=0, f(2)=1

sum = 0

for i in range(n-2): #f(n=3) = f(1) + f(2), once = range(1)

n1, n2 = n2, n1+n2

sum = n1 + n2

return sum

if __name__== "__main__":

print fb(10)

'''#testing range

for i in range(1):

print i #print once, i = 0

'''

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