#include<bits/stdc++.h>
using namespace std;
int n,m,a[105][15],vis[5000005];
struct node
{
	int zt,step;
};
queue <node> q;
int bfs()
{
	node q1;
	q1.step=0;
	q1.zt=(1<<n)-1;
	q.push(q1);
	vis[q1.zt]=1;
	while (!q.empty())
	{
		node fir=q.front();
		q.pop();
		if (fir.zt==0) return fir.step;
		for (int i=1;i<=m;i++)
		{
			int nx=fir.zt;
			for (int j=1;j<=n;j++)
			{
				if (a[i][j]==1&&(nx&(1<<(j-1)))) nx^=(1<<(j-1));
				if (a[i][j]==-1&&!(nx&(i<<(j-1)))) nx|=(1<<(j-1));
			}
			if (vis[nx]==0)
			{
				node now;
				now.step=fir.step+1;
				now.zt=nx;
				q.push(now);
				vis[nx]=1;
			}
		}
	}
	return -1;
}
int main ()
{
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);
	cin>>n>>m;
	for (int i=1;i<=m;i++)
	{
		for (int j=1;j<=n;j++)
		{
			cin>>a[i][j];
		}
	}
	cout<<bfs();
	return 0;
}