def solution(task, n):
    dp = [0.0]*(n+1)
    if n == 0:
        return 0.0
    if n == 1:
        return task[0][0]
    dp[1] = task[0][0]
    for i in range(2, n+1):
        dp[i] = max(dp[i-1]+task[i-1][0], dp[i-2]+task[i-1][1])
    return dp[-1]
if __name__ == '__main__':
    n = int(input())
    task = []
    for i in range(n):
        task.append(list(map(float, input().split())))
    result = solution(task, n)
    print(result)