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#include<stdio.h>
#include<iostream>
#include<vector>
//#include<string>
//#include<map>
//#include<complex>
//#include<stack>
//#include<list>
//#include<set>
//#include<bitset>
//#include<set>
//#include<iterator>
#include<cmath>
//#include<queue>
//#include<time.h>
//#include<string.h>
//#include<fstream>
//#include<sstream>
#include<algorithm>

using namespace std;

#define REP( x,y ) for( int x=0; x<(y); x++ )
#define FORD( x,y,z ) for( int x=y; x>=(z); x-- )
#define FOR(x,b,e) for( int x = b; x <= (e); ++x )
#define SIZE(v) (int)v.size()
#define ALL(c) c.begin(),c.end()
#define VAR(v,n) __typeof(n) v=(n)
#define FOREACH(i,c) for( VAR(i,c.begin());i!=c.end();++i )
#define PB push_back
#define MP make_pair
#define ST first
#define ND second
#define WRITE( V ){ FOREACH(it,V) cout << *it << ", "; cout << endl; }
#define WRITE_ALL(V,s,t) { cout << s << endl;  REP( i,SIZE(V) ){ cout  << i << " ---- ";  FOREACH(it,V[i]) cout << *it+t << ", "; cout << endl;     } }
#define WRP(p) p.ST << " " << p.ND
#define CLEAR( dst,quant ) memset( dst,0, (quant)*sizeof( __typeof(*dst) ) );
#define WAR if( show_help )
#define ENDL(x) REP(crow,(x)) cout << endl;

typedef long long LL;
const bool show_help = 1;
const LL INF = 10000000000001;
LL N,M,K,a,b,c,y,t,w,l_zest;
const long double EPS = 1e-11;
typedef vector<double> VD;
typedef pair<double,LL> PDI;
typedef pair<double, double> PDD;
typedef vector<bool> VB;
typedef vector<LL> VI;
typedef vector< VI > VVI;
typedef pair<LL,LL> PII;
//typedef map< PII, bool > MPIIB;
typedef pair<LL,LL> PLL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef vector<PII> VPII;



struct FAU{
	int *p,*w;
	FAU( int n ) : p(new int[n]), w(new int[n]) {
		REP(x,n) p[x] = w[x] = -1;
	}
	~FAU(){
		delete[] p;
		delete[] w;
	}
	
	int Find( int x ){
		return ( p[x]<0 ) ? x : p[x] = Find( p[x] );
	}
	
	void Union( int x, int y ){
		if( (x = Find(x)) == (y = Find(y)) ) return;
		if( w[x] > w[y] ) p[y] = x;
		else p[x] = y;
		if( w[x] == w[y] ) w[y]++;
	}
	
};

typedef LL wtype;
typedef vector<wtype> VWT;
typedef vector<VWT> VVWT;

VVI V;
VVWT W;

struct Edge{
	Edge( int a1, int b1, wtype w1 ) : a(a1), b(b1), w(w1){}
	int a,b;
	wtype w;
	bool operator<( const Edge & e1 )const{
		return w < e1.w;
	}
};

// funkcja przyjmuje jako parametr graf, a zwraca graf(minimalne drzewo rozpinajace) :)
pair<VVI,VVWT> KruskalMst( VVI & V, VVWT & W ){
	VVI v(SIZE(V));
	VVWT w(SIZE(W));
	FAU fau(SIZE(V));
	vector<Edge> ed;
	REP(i,SIZE(V)) REP(k,SIZE(V[i])) ed.PB( Edge( i,V[i][k], W[i][k] ) );
	sort( ALL(ed) );
	int x,y;
	REP(i,SIZE(ed)){
		if( (x = fau.Find( ed[i].a ) ) != ( y = fau.Find( ed[i].b ) ) ){
			fau.Union( ed[i].a, ed[i].b );
			v[ed[i].a].PB(ed[i].b);
			v[ed[i].b].PB(ed[i].a);
			w[ed[i].a].PB(ed[i].w);
			w[ed[i].b].PB(ed[i].w);
		}
	}
	
	return MP( v,w );
}



int main(){
	ios_base::sync_with_stdio(0);
	cin >> N;
	
	LL **w = new LL*[N+1];
	REP(i,N+1) w[i] = new LL[N+1];
	REP(i,N+1) REP(k,N+1) w[i][k] = INF;
	
	FOR(i,1,N) FOR(k,i,N) cin >> w[i][k];
	
	V = VVI(N+1);
	REP(i,N+1) REP(k,N+1) V[i].PB(k); // tworze graf pełny
	
	W = VVWT(N+1, VWT(N+1,INF)); // towrze wagi w grafie pełnym
	
	FOR(i,1,N+1) FOR(k,i,N) W[k][i-1] = ( W[i-1][k] = w[i][k] );
	
	REP(i,N+1){
		V[i].erase( V[i].begin() + i );
		W[i].erase( W[i].begin() + i );
	}
	
//	WRITE_ALL(V,"Graf Pełny:",0);
//	WRITE_ALL(W,"Wagi w grafie pełnym",0);
	
	
	pair<VVI, VVWT> P = KruskalMst( V,W );
	
	LL suma = 0;
	VVI V2 = P.ST;
	VVWT W2 = P.ND;
	REP(i,SIZE(V2))	REP(k,SIZE(V2[i])) suma += W2[ i ][ k ];
	suma /= 2;
	
	cout << suma << endl;
	
	
	
	
	return 0;
}