n, m=[int(k) for k in input().split()]
w=[]
for j in range(m):
w.append([int(k) for k in input().split()])
q={}
rho={}
for j in range(m):
if w[j][0] in q:
q[w[j][0]].append(w[j][1])
else:
q[w[j][0]]=[w[j][1]]
if w[j][1] in q:
q[w[j][1]].append(w[j][0])
else:
q[w[j][1]]=[w[j][0]]
for j in q.keys():
rho[j]=set(q[j])
c={}
for j in q.keys():
c[j]=len(q[j])
mn=10**100
for j in q.keys():
for k in range(c[j]-1):
for l in range(k, c[j]):
if q[j][k] in rho[q[j][l]]:
mn=min(mn, c[j]+c[q[j][k]]+c[q[j][l]])
if mn>=10**100:
print(-1)
else:
print(mn-2*3)#include <bits/stdc++.h>
using namespace std;
#define TASK "TEST"
#define lint long long int
#define sz(v) (int(v.size()))
#define ynif(c) cout << ((c) ? "YES\n" : "NO\n")
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define exetime cerr << "Time elapsed: " << (1.0 * clock() / CLOCKS_PER_SEC) << "s"
bool know[4043][4043];
int n, m, deg[4043], u, v, Z;
vector <int> a[4043];
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL); cout.tie(NULL);
if (fopen(TASK".INP", "r")) {
freopen(TASK".INP", "r", stdin);
freopen(TASK".OUT", "w", stdout);
}
cin >> n >> m;
for (int i = 1; i <= m; i++) {
cin >> u >> v;
deg[u]++;
deg[v]++;
know[u][v] = know[v][u] = 1;
a[u].push_back(v);
a[v].push_back(u);
}
Z = -1;
for (int i = 1; i <= n; i++)
for (int j : a[i])
for (int k : a[i])
if (j != k && know[j][k]) {
int rec = deg[i] + deg[j] + deg[k] - 6;
if (Z == -1) Z = rec;
else Z = min(Z, rec);
}
cout << Z;
return exetime, 0;
}1650C - Weight of the System of Nested Segments | 1097A - Gennady and a Card Game |
248A - Cupboards | 1641A - Great Sequence |
1537A - Arithmetic Array | 1370A - Maximum GCD |
149A - Business trip | 34A - Reconnaissance 2 |
59A - Word | 462B - Appleman and Card Game |
1560C - Infinity Table | 1605C - Dominant Character |
1399A - Remove Smallest | 208A - Dubstep |
1581A - CQXYM Count Permutations | 337A - Puzzles |
495A - Digital Counter | 796A - Buying A House |
67A - Partial Teacher | 116A - Tram |
1472B - Fair Division | 1281C - Cut and Paste |
141A - Amusing Joke | 112A - Petya and Strings |
677A - Vanya and Fence | 1621A - Stable Arrangement of Rooks |
472A - Design Tutorial Learn from Math | 1368A - C+= |
450A - Jzzhu and Children | 546A - Soldier and Bananas |