def main():
    n = int(input())
    inf = 1<<60
    dp = [0, -inf]
    for _ in range(n):
        p, a = list(map(int, input().split()))
        dp = [max(dp[0]+p, dp[1]+2*p), max(dp[0]+a, dp[1]+2*a)]
    return max(dp)

print(main())