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#include<cstdio>
#include<algorithm>
#include<iostream>
#include<vector>
#include<queue>
#include<string>
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define N 2020
using namespace std;

int n,a,ojc[N],size[N];
long long wyn;
vector<pair<int,pair<int,int> > > kraw;

int find(int x){
    if(ojc[x]==x) return x;
    else return ojc[x]=find(ojc[x]);
}
void uni(int x,int y){
    if(size[x]<size[y]){
        ojc[x]=y;
        size[y]+=size[x];
    }
    else{
        ojc[y]=x;
        size[x]+=size[y];
    }
}

int main(){
    scanf("%d",&n);
    for(int i=0;i<=n;i++){
        ojc[i]=i;
        size[i]=1;
    }
    for(int i=1;i<=n;i++) for(int j=1;j<=n-i+1;j++){
        scanf("%d",&a);
        kraw.pb(mp(a,mp(i-1,i+j-1)));
    }
    sort(kraw.begin(),kraw.end());
    for(int i=0;i<kraw.size();i++){
        if(find(kraw[i].se.fi)!=find(kraw[i].se.se)){
            wyn+=kraw[i].fi;
            uni(find(kraw[i].se.fi),find(kraw[i].se.se));
        }
    }
    printf("%lld",wyn);
}