N = int(input())
num = []
for _ in range(N):
    x,y = list(map(int,input().split()))
    num.append((x,y))

INF = 10**18
dp = [[-INF,-INF] for _ in range(N+1)]
dp[1][0] = 0
dp[1][1] = 0
for i in range(1,N):
    v = num[i][0] if num[i][0] == num[i][1] else 0

    # xy
    dp[i+1][0] = max(dp[i][0] + num[i][0] * (num[i][0] == num[i-1][1]),
                     dp[i][1] + num[i][0] * (num[i][0] == num[i-1][0])) + v

    # yx
    dp[i+1][1] = max(dp[i][0] + num[i][1] * (num[i][1] == num[i-1][1]),
                     dp[i][1] + num[i][1] * (num[i][1] == num[i-1][0])) + v

print(max(dp[-1]))