/** \brief poj 1502--Dijkstra
 *
 * \ date 2014/7/15
 * \ state AC
 *  *
 */

#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>

using namespace std;

#define inf 0x03f3f3f3f
const int MAXN=101;
int n;
int cost[MAXN][MAXN];
int path[MAXN];
int vis[MAXN];
int lowcost[MAXN];

void input()
{
    char st[100];
    for (int i = 1; i < n; i++)
        for (int j = 0; j < i; j++)
        {
            scanf("%s", st);
            if (st[0] == 'x')
                cost[i][j] = cost[j][i] = inf;
            else
                cost[i][j] = cost[j][i] = atoi(st);
        }
}

void Dijkstra(int cost[][MAXN],int lowcost[MAXN],int n,int beg)
{
    int i,j,Min;
    memset(vis,0,sizeof(vis));
    vis[beg]=1;

    for(i=0;i<n;i++)
    {
        lowcost[i]=cost[beg][i];
        path[i]=beg;
    }

    lowcost[beg]=0;
    path[beg]=-1;//树根的标记
    int pre=beg;
    for(i=1;i<n;i++)
    {
        Min=inf;
        for(j=0;j<n;j++)
            //下面的加法可能导致溢出，inf不能取太大
            if(vis[j]==0 && lowcost[pre]+cost[pre][j]<lowcost[j])
        {
            lowcost[j]=lowcost[pre]+cost[pre][j];
            path[j]=pre;
        }

        for(j=0;j<n;j++)
            if(vis[j]==0 && lowcost[j]<Min)
        {
            Min=lowcost[j];
            pre=j;
        }

        vis[pre]=1;
    }
}

int main()
{
    //cout << "Hello world!" << endl;
    //freopen("input.txt","r",stdin);
    cin>>n;
    input();
    Dijkstra(cost,lowcost,n,0);
    int ans = 0;
    for (int i = 0; i < n; i++)
        ans = max(ans, lowcost[i]);
    cout<<ans<<endl;
    return 0;
}