N = int(input())
prev = {-1: 0}
for _ in range(N):
    x, y = map(int, input().split())
    nprev = {}
    mx = max(prev.values())
    if x == y:
        if x in prev:
            nprev[x] = max(mx, prev[x] + 2 * x)
        else:
            nprev[x] = mx + x
        prev = nprev
        continue
    if x in prev:
        nprev[y] = max(mx, prev[x] + x)
    else:
        nprev[y] = mx
    if y in prev:
        nprev[x] = max(mx, prev[y] + y)
    else:
        nprev[x] = mx
    prev = nprev
print(max(prev.values()))