class BIT():
    """一点加算、区間取得クエリをそれぞれO(logN)で答える
    add: i番目にvalを加える
    get_sum: 区間[l, r)の和を求める
    i, l, rは0-indexed
    """
    def __init__(self, n):
        self.n = n
        self.bit = [0] * (n + 1)

    def _sum(self, i):
        s = 0
        while i > 0:
            s += self.bit[i]
            i -= i & -i
        return s

    def add(self, i, val):
        """i番目にvalを加える"""
        i += 1
        while i <= self.n:
            self.bit[i] += val
            i += i & -i

    def get_sum(self, l, r):
        """区間[l, r)の和を求める"""
        return self._sum(r) - self._sum(l)


n = int(input())
a = list(map(int, input().split()))

b = [0] * n
for i in range(n):
    b[i] = a[2 * i] - a[2 * i + 1]
    
bit = BIT(n)
for i in range(n):
    bit.add(i, b[i])
    
ans = 0
for i in range(n + 1):
    ans = max(ans, bit.get_sum(0, i) - bit.get_sum(i, n))
print(ans)