#include<bits/stdc++.h>
using namespace std;

typedef pair<int,int> PII;

int m, n;
const int N = 510;
int e[N], ne[N], h[N], idx;
int dist[N], st[N];

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}

void dj()
{
    priority_queue<PII, vector<PII>, greater<PII>> q;
    q.push({0,1});
    dist[1] = 0;
    while(q.size())
    {
        auto x = q.top();
        q.pop();
        int va = x.second, di = x.first;
        if(st[va]) continue;
        st[va] = 1;
        for(int i = h[va]; i != -1; i = ne[i])
        {
            int j = e[i];
            if(dist[j] > di+1)
            {
                dist[j] = di+1;
                q.push({dist[j], j});
            }
        }
    }
}

int main(void)
{
    memset(h, -1, sizeof h);
    memset(dist, 0x3f, sizeof dist);
    cin >> m >> n;
    char x;
    x = getchar();
    for(int i = 1; i <= n; ++i)
    {
        x = getchar();
        int num = 0;
        if(x == EOF) break;
        vector<int> qq;
        while(x != '\n' && x != EOF)
        {
            if(x != ' ') num = num*10+x-'0';
            else
            {
                for(int i = 0; i < qq.size(); ++i) add(qq[i], num);
                qq.push_back(num);
                //printf("%d %d\n", i, num);
                num = 0;
            }
            x = getchar();
        }
        for(int i = 0; i < qq.size(); ++i) add(qq[i], num);
        qq.push_back(num);
        num = 0;
    }
    dj();
    if(dist[n] == 0x3f3f3f3f) printf("NO");
    else printf("%d\n", dist[n]-1);

    return 0;
}