N=int(input())
d = []
for _ in range(N):
    x,y=map(int,input().split())
    d.append((x,y))
inf = 10**18
dp=[[-inf,-inf] for _ in range(N)]
x,y = d[0]
c = 0
if x == y:
    c = x
dp[0] = [c,c]
for i in range(N-1):
    for k in range(2):
        for k2 in range(2):
            x1 = d[i][k]
            x2 = d[i+1][1-k2]
            if d[i+1][0] == d[i+1][1]:
                d_ = d[i+1][0]
            else:
                d_ = 0
            if x1 == x2:
                dp[i+1][k2] = max(dp[i+1][k2],dp[i][k]+x1+d_)
            else:
                dp[i+1][k2] = max(dp[i+1][k2],dp[i][k]+d_)
print(max(dp[-1]))