#include <iostream>

#include <cstring>

#include <cstdio>

using namespace std;

const int maxn =  + ;

const int inf = 0x3f3f3f3f;

int n, mp[maxn][maxn], dis[maxn];

bool vis[maxn];

inline int max( int a, int b ){

    return a>b ? a:b;

}

inline int min( int a, int b ){

    return a<b ? a:b;

}

inline int dij(){

    memset( vis, , sizeof(vis) );

    memset( dis, inf, sizeof(dis) );

    dis[] = ;

    for( int i=; i<n; i++ ){

        int minid, MIN = inf;

        for( int j=; j<=n; j++ ) if( !vis[j] && MIN>dis[j] ) MIN = dis[minid=j];

        vis[minid] = ;

        for( int j=; j<=n; j++ ) if( !vis[j] ) dis[j] = min( dis[j], dis[minid]+mp[minid][j] );

    }

    int res = -inf;

    for( int i=; i<=n ;i++ )

        res = max( res, dis[i] );

    return res;

}

int main(){

    // freopen("in.txt", "r", stdin);

    scanf("%d", &n);

    for( int i=; i<=n; i++ )

        for( int j=; j<i; j++ ){

            char s[];

            scanf("%s", s);

            if( s[]=='x' ) mp[i][j] = mp[j][i] = inf;

            else{

                int w = ;

                for( int k=; s[k]; k++ ){

                    w *= ;

                    w += s[k]-'';

                }

                mp[i][j] = mp[j][i] = w;

            }

        }

    printf("%d\n", dij());

    return ;

}