fib(0)=0
fib(1)=1
fib(2)=1
fib(3)=2
fib(4)=3
fib(5)=5
fib(6)=8
fib(7)=13
fib(8)=21
fib(9)=34
fib(10)=55
fib(11)=89
fib(12)=144
fib(13)=233
fib(14)=377
fib(15)=610
fib(16)=987
fib(17)=1597
fib(18)=2584
fib(19)=4181
fib(20)=6765
fib(21)=10946
fib(22)=17711
fib(23)=28657
fib(24)=46368
fib(25)=75025
fib(26)=121393
fib(27)=196418
fib(28)=317811
fib(29)=514229
fib(30)=832040
fib(31)=1346269
fib(32)=2178309
fib(33)=3524578
fib(34)=5702887
fib(35)=9227465
fib(36)=14930352
fib(37)=24157817
fib(38)=39088169
fib(39)=63245986
fib(40)=102334155
fib(41)=165580141
fib(42)=267914296
fib(43)=433494437
fib(44)=701408733
fib(45)=1134903170
fib(46)=1836311903
fib(47)=2971215073
fib(48)=4807526976
fib(49)=7778742049
fib(50)=12586269025