#!/bin/python3
import sys

def derivative(numbers):
  output = []
  for x in range(len(numbers) - 1):
    output.append(numbers[x+1] - numbers[x])
  return output

output = 0
for line in sys.stdin:
  line = line.strip()

  numbers = [int(x) for x in line.split()]
  derivatives = [numbers]
  while len([x for x in derivatives[-1] if x != 0]) > 0:
    derivatives.append(derivative(derivatives[-1]))

  prediction = 0
  sign = 1
  for d in derivatives:
    prediction += d[0] * sign
    sign *= -1

  output += prediction

print(f">> {output}")