N = int(input())
H = list(map(int, input().split()))

bottom = 0
ans = 0

for i in range(N-1, -1, -1):
    h = H[i]
    if i%2==0:
        #水色
        ans += max(0, h-bottom)
    else:
        pass

    bottom = max(bottom, h)
print(ans)
"""
5
7 3 2 4 5
"""