N = int(input())

xs = []
for _ in range(N):
    X, Y = map(int, input().split())
    xs.append((X, Y))

dp = [0, 0]
x, y = xs[0]
if x == y:
    dp = [x, x]

for i in range(1, N):
    px, py = xs[i-1]
    x, y = xs[i]

    pp = [0, 0]
    dp, pp = pp, dp
    # x -> y
    dp[0] = max(dp[0], pp[0] + (x if x == py else 0))
    dp[0] = max(dp[0], pp[1] + (x if x == px else 0))
    # y -> x
    dp[1] = max(dp[1], pp[0] + (y if y == py else 0))
    dp[1] = max(dp[1], pp[1] + (y if y == px else 0))

ans = max(dp)
print(ans)