import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

n=II()
xy=LLI(n)
dp=[0,0]
pre=[0,0]
s=0
for i in range(n-1):
    if xy[i][0]==xy[i][1]:s+=xy[i][0]
    pre,dp=dp,pre
    score=[[0,0],[0,0]]
    for d in range(2):
        for e in range(2):
            if xy[i][d]==xy[i+1][e]:
                score[d][e]=xy[i][d]
    dp[0]=max(pre[0]+score[0][1],pre[1]+score[1][1])
    dp[1]=max(pre[0]+score[0][0],pre[1]+score[1][0])
if xy[-1][0]==xy[-1][1]:s+=xy[-1][0]
print(max(dp)+s)