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#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
#define f first
#define s second

const int size = 3000000;

pair<int, pair<int, int> > T[size];

int n, ran[size], sup[size];

int find(int x) {
	if(sup[x] == x) return x;
	return sup[x] = find(sup[x]);
}

int myUnion (int x, int y) {
	int a = find(x), b = find(y);
	if(ran[a] < ran[b]) sup[a] = b;
	else if(ran[a] > ran[b]) sup[b] = a;
	else {
		sup[a] = b;
		ran[b]++;
	}
}

int main() {
	int counter = 0;
	scanf("%d", &n);
	for(int i = n; i>0; i--) {
		for(int j = n-i; j<n; j++) {
			int a;
			scanf("%d", &a);
			T[counter++] = make_pair(a, make_pair(n-i, j+1));
		}
	}
	sort(T, T+counter);
	for(int i = 0; i<=n; i++) {
		ran[i] = 0;
		sup[i] = i;
	}
	long long result = 0;
	counter = 0;
	for(int i = 0; counter<n; i++) {
		int x = T[i].s.f, y = T[i].s.s;
		x = find(x);
		y = find(y);
		if(x != y) {
			result += (long long) T[i].f;
			counter++;
			myUnion(x, y);
		}
	}
	printf("%lld\n", result);
	return 0;
}