n=gets.to_i - 1
a=[1,1,1,0]
b=[1,1,1,0]
def mul a,b
  [a[0]*b[0]+a[1]*b[2], a[0]*b[1]+a[1]*b[3], a[2]*b[0]+a[3]*b[2], a[2]*b[1]+a[3]*b[3]]
end

while n>0
  if n & 1 == 1
    b = mul a,b
  end
  a = mul a,a
  n >>= 1
end
puts b[0]