from math import inf


def main():
    scores_normal = [0]
    scores_bonus = [-inf]

    for idx in range(int(input())):
        p, a = map(int, input().split())
        scores_normal.append(
            max(scores_normal[idx]+p, scores_bonus[idx]+2*p)
        )
        scores_bonus.append(
            max(scores_normal[idx]+a, scores_bonus[idx]+2*a)
        )
    print(max(scores_normal[-1], scores_bonus[-1]))


if __name__ == "__main__":
    main()