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)]
dp[N][0] = dp[N][1] = A[N][0]
for i in range(N-1,0,-1):
    dp[i][0] = A[i][0]+max(dp[i+1][0],dp[i+1][1])
    dp[i][1] = A[i][1]+max(A[i+1][0]+dp[i+1][0],A[i+1][1]+dp[i+1][1])
print(max(dp[1][0],dp[1][1]))