N=int(input())
dp=[[[0,0] for _ in range(2)] for _ in range(N+1)]
dp[0][0]=[0,0]
dp[0][1]=[0,0]
for i in range(N):
    x,y=map(int,input().split())
    s1=dp[i][0][0]
    if dp[i][0][1]==x:s1+=x
    s2=dp[i][1][0]
    if dp[i][1][1]==x:s2+=x
    dp[i+1][0]=[s1,y] if s1>=s2 else [s2,y]
    if x==y:dp[i+1][0][0]+=x
    s1=dp[i][0][0]
    if dp[i][0][1]==y:s1+=y
    s2=dp[i][1][0]
    if dp[i][1][1]==y:s2+=y
    dp[i+1][1]=[s1,x] if s1>=s2 else [s2,x]
    if x==y:dp[i+1][1][0]+=x
print(max(dp[N][0][0],dp[N][1][0]))