require 'set'
require 'rational'

$buf = []
def fill_buf; (s = gets) ? $buf = s.chomp.split : break while $buf.empty? end
def has_next; fill_buf; !$buf.empty? end
def get; fill_buf; $buf.shift end
def geti; get.to_i end
def getf; get.to_f end
def getss(n = nil); n ? Array.new(n) { get } : begin fill_buf; $buf.shift(1e9) end; end
def getis(n = nil); getss(n).map(&:to_i) end
def getfs(n = nil); getss(n).map(&:to_f) end


while has_next
  b1, b2, b3 = getis
  r = Rational(b3 - b2, b2 - b1)
  d = b2 - r*b1
  # p [r, d] w
  p (b3*r + d).to_i
end