X

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



int main()

{
    // freopen("i.txt","r",stdin);
   // freopen("o.txt","w",stdout);

    int n,m;
    cin>>n>>m;
    bool adj[n+3][n+3];
    int deg[n+3];
    for(int i=1;i<=n+1;i++)
        deg[i]=0;
    for(int i=1;i<=n+1;++i)
        {
            for(int j=1;j<=n+2;++j)
                adj[i][j]=false;
        }


    while(m--)
    {
        int a,b;
        cin>>a>>b;
        adj[a][b]=true;
        adj[b][a]=true;
        deg[a]++;
        deg[b]++;
    }

    int result=100005;
        for(int i=1;i<=n;++i)
        {
            for(int j=i+1;j<=n;++j)
            {
                if(adj[i][j])
                {
                    for(int k=j+1;k<=n;++k)
                    {
                        if(adj[k][i] && adj[k][j])
                            result= min(result,(deg[i]+deg[j]+deg[k]));
                            //cout<<result<<endl;
                             //cout<<i<<" "<<j<<" "<<k<<endl;}
                    }
                }
            }

        }
        if(result==100005)
            cout<<"-1"<<"\n";
        else
            cout<<result-6<<"\n";
}