N = int(input())
prev = {-1: 0}
for _ in range(N):
    x, y = map(int, input().split())
    nprev = {}
    if x in prev:
        nprev[y] = prev[x] + x
    else:
        nprev[y] = max(prev.values())
    if y in prev:
        if x not in nprev:
            nprev[x] = prev[y] + y
        else:
            nprev[x] = max(nprev[x], prev[y] + y)
    else:
        nprev[x] = max(prev.values())
    prev = nprev
print(max(prev.values()))