Диаметър

#include <iostream>
#include <vector>
#include <climits>
#include <algorithm>

using namespace std;

int main() {
    int n, m; cin >> n >> m;
    vector < vector<int> >dist;
    dist.assign(n, vector<int>(n, INT_MAX));
    for (int i = 0; i < m; i++) {
        int u, v; cin >> u >> v;
        --u; --v;

        dist[u][v] = 1;
        dist[v][u] = 1;
    }

    for (int k = 0; k < n; k++) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (dist[i][k] != INT_MAX && dist[k][j] != INT_MAX) {
                    dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
                }
            }
        }
    }

    int ans = INT_MIN;
    for (int i = 0; i < dist.size(); i++) {
        for (int j = 0; j < dist[0].size(); j++) {
            ans = max(ans, dist[i][j]);
        }
    }
    cout << ans << endl;


    return 0;
}