N = int(input())
dist = [[False] * N for _ in range(N)]

level = [0] * N
stage = [0] * N
reg = 0
for i in range(N):
    l, s = map(int, input().split())
    level[i] = l
    stage[i] = s - 1
    dist[i][stage[i]] = True
    dist[i][i] = True

    reg += level[i]

for k in range(N):
    for i in range(N):
        for j in range(N):
            dist[i][j] = dist[i][j] | (dist[i][k] & dist[k][j])

for i in range(N):
    flag = True
    for j in range(i):
        if dist[i][j] and dist[j][i]:
            flag = False
    if not flag:
        continue

    for j in range(N):
        if dist[i][j] and not dist[j][i]:
            flag = False
    if not flag:
        continue

    mincost = 999
    for j in range(i, N):
        if dist[i][j] and dist[j][i]:
            mincost = min(mincost, level[j])

    reg += mincost

print(reg / 2)