#include<cstdio>
#include<cmath>
#include<iostream>
#include<cstring>
#include<iomanip>
#include<cctype>
#include<algorithm>
#define INF 10086110
using namespace std;
int f[10010],sum=0,n,m,k,i,j,num=0;
struct EDg
{
	int u;
	int v;
	int w;
}e[10010];
int getf(int v)
{
	if(f[v]==v)return v;
	else return f[v]=getf(f[v]);	
}
bool cmp(EDg a,EDg b)
{
	if(a.w<b.w)return 1;
	else return 0;
}
int beg()
{
	for(i=1;i<=n;i++)
	f[i]=i;
}
int main()
{
	freopen("mcst.in","r",stdin);
	freopen("mcst.out","w",stdout);
	cin>>n;
	beg();
	for(int i=1;i<=n;i++)
	for(int j=1;j<=n;j++)
	{
		int x;
		cin>>x;
		if(j>=i)
		continue;
		else {
		if(x==-1)continue;
		
		e[++num].v=i;
		e[num].u=j;
		e[num].w=x;
		}
	}
	sort(e+1,e+num+1,cmp);
	int fx,fy;
	for(int i=1;i<=num;i++)
	{
		fx=getf(e[i].v);
		fy=getf(e[i].u);
		if(fx!=fy)
		{
		f[fx]=fy;
	    sum+=e[i].w;
	    
	    }
	}
	cout<<sum;
	return 0;
}