def mul(na, nb)
  a, b, c = na
  d, e, f = nb
  return a*d + b*e, a*e + b*f, b*e + c*f
end

def pow(a, n)
  return a if n == 1
  return pow(mul(a, a), n/2) if n & 1 == 0
  return mul(a, pow(mul(a, a), (n-1)/2))
end

def fib(n)
  return n if n < 2
  return pow([1,1,0], n-1)[0]
end

fib(51)

# => 20365011074

var fib = new Array;
fib[1] = 0;
fib[2] = 1;
function calculate_fib(number) {
for (i = 3; i <= number; i++) {
  fib[i] = fib[i-1] + fib[i-2];
}
return fib[number];
}
document.write(calculate_fib[52]); //32 951 280 099