N = int(input())
A = [0]+[list(map(int, input().split())) for _ in range(N)]
dp = [[0 for _ in range(2)] for _ in range(N+1)]
if A[1][0]==A[1][1]:
    dp[1][0] = A[1][0]
    dp[1][1] = A[1][1]
for i in range(2, N+1):
    if A[i-1][1]==A[i][0]:
        dp[i][0] = dp[i-1][0]+A[i][0]
    elif A[i-1][0]==A[i][0]:
        dp[i][0] = dp[i-1][1]+A[i][0]
    else:
        dp[i][0] = max(dp[i-1][0],dp[i-1][1])
    if A[i-1][1]==A[i][1]:
        dp[i][1] = dp[i-1][0]+A[i][1]
    elif A[i-1][0]==A[i][1]:
        dp[i][1] = dp[i-1][1]+A[i][1]
    else:
        dp[i][1] = max(dp[i-1][0],dp[i-1][1])
print(max(dp[N][0], dp[N][1]))