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#include <cstdio>
#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <stack>
#include <list>
#include <queue>
#include <deque>
#include <cctype>
#include <string>
#include <vector>
#include <sstream>
#include <iterator>
#include <numeric>
#include <cmath>
using namespace std;

typedef vector <int > VI;
typedef vector < VI > VVI;
typedef long long LL;
typedef vector < LL > VLL;
typedef vector < double > VD;
typedef vector < string > VS;
typedef pair<int,int> PII;
typedef vector <PII> VPII;
typedef istringstream ISS;

#define ALL(x) x.begin(),x.end()
#define REP(i,n) for (int i=0; i<(n); ++i)
#define FOR(var,pocz,koniec) for (int var=(pocz); var<=(koniec); ++var)
#define FORD(var,pocz,koniec) for (int var=(pocz); var>=(koniec); --var)
#define FOREACH(it, X) for(__typeof((X).begin()) it = (X).begin(); it != (X).end(); ++it)
#define PB push_back
#define PF push_front
#define MP(a,b) make_pair(a,b)
#define ST first
#define ND second
#define SIZE(x) (int)x.size()

const int N = 2011;
int t[N][N];

int main(){
  int n;
  scanf("%d",&n);
  REP(i,n) FOR(j,i,n-1) scanf("%d",t[i]+j);

  LL res = 0;
  REP(i,n) {
    int best = i;
    for (int j = i; j < n; ++j) if (t[i][best] > t[i][j]) best = j;
    int x = t[i][best];
    res += x;
    for (int j = i; j < n; ++j) if (j <= best) {
      t[j+1][best] = min(t[j+1][best], t[i][j]);
    } else {
      t[best+1][j] = min(t[best+1][j], t[i][j]);
    }
  }
  printf("%lld\n", res);
  return 0;
}