n = int(input()) positions = [[0 for h in range(n)] for g in range(n)]

a = b = c =1 while a != 0 and b != 0 and c != 0: a, b, c = map(int, input().split()) if 0 < a <= n and 0 < b <= n: # 确保输入在有效范围内 positions[a - 1][b - 1] = c

count = 0 i = j = 0 for num in range(2): i=j=0 tag = 0

while tag < 2 * n:
    sumx = sumy = 0

    # 计算 sumx
    if i < n:  # 确保 i 在有效范围内
        for d in range(j + 1, n):
            if d < n:  # d 的有效性检查
                sumx += positions[i][d]

    # 计算 sumy
    if j < n:  # 确保 j 在有效范围内
        for f in range(i + 1, n):
            if f < n:  # f 的有效性检查
                sumy += positions[f][j]
    # 更新 i 和 j
    if sumx > sumy:
        j += 1
    elif sumx < sumy:
        i += 1
    else:
        i += 1
        j += 1

    # 检查 i 和 j 是否在有效范围内
    if i < n and j < n:
        if positions[i][j] != 0:
            count += positions[i][j]
            positions[i][j] = 0
    tag += 1

print(count)