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