#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cstring>
using namespace std;
int prim();
int n,g[1510][1510];
int main()
{
	freopen("mcst.in","r",stdin);
	freopen("mcst.out","w",stdout);
	memset(g,127,sizeof(g));
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<=n;j++)
		{
			int k;
			scanf("%d",&k);
			if(k==-1)continue;
			g[i][j]=g[j][i]=k;
		}
	}
	printf("%d",prim());
}
int prim()
{
	int j,minn,mst=0,low[1510],set[1510],used[1510];
	memset(low,127,sizeof(low));
	for(int i=1;i<=n;i++)
	{
		low[i]=g[1][i];
		used[i]=0;
		set[i]=1;
	}
	used[1]=1;
	for(int i=1;i<n;i++)
	{
		j=0;minn=0x7f7f7f7f;
		for(int k=2;k<=n;k++)
		{
			if(!used[k]&&low[k]<minn)
			{
				minn=low[k];
				j=k;
			}
		}
		used[j]=1;
		mst+=minn;
		for(int i=2;i<=n;i++)
		{
			if(!used[i]&&low[i]>g[j][i])
			{
				low[i]=g[j][i];
				set[i]=j;
			}
		}
	}
	return mst;
}