import itertools

N = int(input())
LS = []
for i in range(N):
    LS.append(list(map(int, input().split())))

turn = [x for x in range(N)]
turn_list = list(itertools.permutations(turn, N))

ans = float('inf')
for t in turn_list:
    sum = 0
    area = [False] * N
    for t_i in t:
        if area[LS[t_i][1] - 1]:
            sum += LS[t_i][0] / 2
        else:
            sum += LS[t_i][0]
        area[t_i] = True

    if ans > sum:
        ans = sum

print(ans)