import sys

L = sys.stdin.read().splitlines()
S = 0
for report in L:
    l = [int(r) for r in report.split(' ')]
    S+=l[-1]

    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])
            
        S+=m[-1]
        l = list(m)

print(S)