N=int(input())
dp=[[[0,0,0] for _ in range(2)] for _ in range(N+1)]
dp[0][0]=[0,0,0]
dp[0][1]=[0,0,0]
for i in range(N):
    x,y=map(int,input().split())
    tmp1=dp[i][0][2] if dp[i][0][1]!=x else dp[i][0][2]+x
    tmp2=dp[i][1][2] if dp[i][1][1]!=x else dp[i][1][2]+x
    if tmp1>=tmp2:dp[i+1][0]=[x,y,tmp1]
    else:dp[i+1][0]=[x,y,tmp2]
    tmp1=dp[i][0][2] if dp[i][0][1]!=y else dp[i][0][2]+y
    tmp2=dp[i][1][2] if dp[i][1][1]!=y else dp[i][1][2]+y
    if tmp1>=tmp2:dp[i+1][1]=[y,x,tmp1]
    else:dp[i+1][1]=[y,x,tmp2]
print(max(dp[N][0][2],dp[N][1][2]))