import sys

L = sys.stdin.read().splitlines()
S = 0
for report in L:
    l = [int(r) for r in report.split(' ')]
    prem = [l[0]]

    while not all(v == 0 for v in l):
        m = []
        for i in range(0,len(l)-1):
            m.append(l[i+1] - l[i])
            
        prem.append(m[0])
        l = list(m)

    s = prem[0]
    signe = -1
    for a in prem[1:]:
        s+=(a*signe)
        signe *= -1
    S+=s

print(S)