using namespace std;
#include                    <bits/stdc++.h>
#define     DB(x)           cerr << #x << " is " << (x) << endl;
#define     FIO             ios::sync_with_stdio(false);// cin.tie(nullptr); cout.tie(nullptr) // ===  === === === === === ===>
#define     pb              push_back
#define     fs              first
#define     sc              second
#define     endl            "\n"
typedef     long long           ll;
typedef     long double         ld;
int const mxn = 2e3+2;
int const mod = 1e9+7;

int n, m, ans=-1;
vector<int> E[mxn];
vector<int> dd(mxn);
queue<int> Q;

int cal(int u){
    Q.push(u);
    dd[u] = 1;
    while (Q.size()){
        u = Q.front();
        Q.pop();
        for (auto v: E[u]){
            if (dd[v]) continue;
            dd[v] = dd[u]+1;
            Q.push(v);
        }
    }
    int f = 0, mx = 0;
    for (int i=1; i<=n; ++i){
        if (!dd[i]) f = 1;
        mx = max(mx,dd[i]);
        dd[i] = 0;
    }
    if (f) return -1;
    return mx;
}

void SOL(){
    cin >> n >> m;
    for (int i=1; i<=m; ++i){
        int x, y; cin >> x >> y;
        E[x].pb(y);
        E[y].pb(x);
    }
    for (int i=1; i<=n; ++i){
        ans = max(ans,cal(i));
    }
    if (ans == -1){
        cout << "=[";
    } else {
        cout << "=] " << ans-1;
    }
}
/*
*/
int main(){FIO; SOL(); return 0;}