n = int(input())
x1, y1 = map(int, input().split())
dp0 = dp1 = 0
for _ in range(n - 1):
    x2, y2 = map(int, input().split())
    dp0, dp1 = max(dp0 + (y1 if y1 == x2 else 0), dp1 + (x1 if x1 == x2 else 0)), max(dp0 + (y1 if y1 == y2 else 0), dp1 + (x1 if x1 == y2 else 0))
    x1, y1 = x2, y2
print(max(dp0, dp1))