N = int(input())
XY = [list(map(int, input().split())) for _ in range(N)]

INF = 1<<60

dp = [[-INF]*2 for _ in range(N)]
dp[0][0] = 0
dp[0][1] = 0
if XY[0][0] == XY[0][1]:
    dp[0][0] = XY[0][0]
    dp[0][1] = XY[0][1]
for i in range(1, N):
    for j in range(2):
        pre = XY[i-1][j^1]
        for k in range(2):
            now = XY[i][k]
            if pre == now:
                dp[i][k] = max(dp[i][k], dp[i-1][j]+pre)
            else:
                dp[i][k] = max(dp[i][k], dp[i-1][j])
    if XY[i][0] == XY[i][1]:
        dp[i][0] += XY[i][0]
        dp[i][1] += XY[i][1]

print(max(dp[-1]))