import sequtils,strutils,algorithm

type bound = tuple[a : int,b : int,value : int]
var
    N = stdin.readline.parseInt
    A = newSeqWith(N,newSeq[int](0))
    cnt : int
    T : seq[int]
    unit : bound
    flag = newSeqWith(N,false)
    Units = newSeq[bound](0)
for n in 0..<N:
    A[n] = stdin.readline.split.map(parseInt)

T = @[]
for k in 1..<N:
    for j in 0..<k:
        unit = (k,j,-A[k][j])
        Units.add(unit)
Units = Units.sortedByIt(it.value)

cnt = 0
for u in Units:
    if flag[u.a] == false and flag[u.b] == false:
        cnt -= u.value
        flag[u.a] = true
        flag[u.b] = true
echo cnt