#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=2005;
const ll inf=1e12;
ll e[N][N];
int n;
ll d[N];
ll ans;
bool vis[N];
int main(){
	freopen("nosay.in","r",stdin);
    freopen("nosay.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	cin>>n;
	for(int i(1);i<=n;++i){
		d[i]=inf;
		for(int j(1);j<=n;++j)
		e[i][j]=inf;
	}
	for(int i(1);i<=n;++i){
		int len=n-i+1;
		for(int j(1);j<=len;++j){
			ll w;
			cin>>w;
			e[i-1][i+j-1]=e[i+j-1][i-1]=w;
		}
	}
	d[0]=0;
	for(int i(0);i<=n;++i){
		ll hs=inf,u=0;
		for(int j(0);j<=n;++j){
			if(!vis[j]&&d[j]<hs){
				hs=d[j];
				u=j;
			}
		}
		vis[u]=true;
		ans+=hs;
		for(int j(0);j<=n;++j){
			if(!vis[j]&&e[u][j]<d[j]){
				d[j]=e[u][j];
			}
		}
	}
	cout<<ans<<"\n";
	
	return 0;
}