#include<cstdio>
#include<algorithm>
#define N 1505
using namespace std;
int n,m,f[N],x,ans;
struct edge{int u,v,w;bool operator<(edge y){return w<y.w;}}a[N];
int fd(int x){return x^f[x]?f[x]=fd(f[x]):x;}
void mg(int x,int y){f[fd(x)]=fd(y);}
int main()
{
    freopen("mcst.in","r",stdin);freopen("mcst.out","w",stdout);
    scanf("%d",&n);
    for(int i=1;i<=n;i++)f[i]=i;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
        {
            scanf("%d",&x);
            if(~x)a[++m]={i,j,x};
        }
    sort(a+1,a+m+1);
    n--;
    for(int i=1;i<=m&&n;i++)
    {
        int u=a[i].u,v=a[i].v,w=a[i].w;
        if(fd(u)==fd(v))continue;
        mg(u,v);
        ans+=w;
    }
    printf("%d",ans);
    return 0;
}