#include <cstdio>
#include <cstring>
#include <iostream>
#include <bitset>
#include <queue>
using namespace std;
int diss[502][502], a[502];
int fir[502], nxt[500002], to[500002], tot;
inline void add(int a, int b) {
    nxt[++tot] = fir[a];
    fir[a] = tot;
    to[tot] = b;
}
int dis[502];
struct node {
    int to, w;
    bool operator < (node x) const {
        return w > x.w;
    }
};
int main() {
    //freopen("__.in", "r", stdin);
    //freopen("__.out", "w", stdout);
    int m, n;
    scanf("%d%d", &m, &n);
    char c = getchar();
    for (int i = 1; i <= m; ++i) {
        c = getchar();
        int tot = 0;
        while (c != '\n') {
            int x = 0;
            while (c < '0' || c > '9') {
                c = getchar();
            }
            while (c >= '0' && c <= '9') {
                x = (x << 3) + (x << 1) + (c ^ '0');
                c = getchar();
            }
            a[++tot] = x;
        }
        for (int j = 1; j <= tot; ++j) {
            for (int k = j + 1; k <= tot; ++k) {
                diss[a[j]][a[k]] = 1;
            }
        }
    }
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= n; ++j) {
            if (diss[i][j]) {
                add(i, j);
            }
        }
    }
    memset(dis, 0x3f, sizeof dis);
    dis[1] = 0;
    bitset<502> bo;
    priority_queue<node> team;
    bo.reset();
    team.push(node{1, 0});
    while (!team.empty()) {
        node x = team.top();
        team.pop();
        if (bo[x.to]) {
            continue;
        }
        bo[x.to] = 1;
        for (int i = fir[x.to]; i; i = nxt[i]) {
            if (dis[to[i]] > dis[x.to] + 1) {
                dis[to[i]] = dis[x.to] + 1;
                team.push(node{to[i], dis[i]});
            }
        }
    }
    if (dis[n] != 0x3f3f3f3f) printf("%d\n", dis[n] - 1);
    else puts("NO");
    return 0;
}