import sys

L = [list(map(int,l.split(' '))) for l in sys.stdin.read().splitlines()]

def extrapolate(L):
    if all(not a for a in L):
        return [0]+L
    M = [b-a for a,b in zip(L,L[1:])]
    return [L[0]-extrapolate(M)[0]]+L

print(sum(extrapolate(l)[0] for l in L))