Problem C. Острова

#include <set>
#include <cmath>
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;



int get_parent(int v, vector <int>& parent, int& father, vector <int>& sz) {
    if (parent[v] == v) {
        father = v;
        return v;
    }
    return get_parent(parent[v], parent, father, sz);
    parent[v] = father;
}

void unite(int fr, int to, vector <int>& parent, vector <int>& sz, int& max_sz) {
    int fath_1 = -1;
    int dad_1 = get_parent(fr, parent, fath_1, sz);
    int fath_2 = -2;
    int dad_2 = get_parent(to, parent, fath_2, sz);
    if (dad_1 == dad_2) {
        return;
    }
    else if (sz[dad_1] <= sz[dad_2]) {
        parent[dad_1] = dad_2;
        sz[dad_2] += sz[dad_1];
        if (sz[dad_2] > max_sz) {
            max_sz = sz[dad_2];
        }
    }
    else {
        parent[dad_2] = dad_1;
        sz[dad_1] += sz[dad_2];
        if (sz[dad_1] > max_sz) {
            max_sz = sz[dad_1];
        }
    }
}


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int n, m;
    cin >> n >> m;
    vector <int> parent(n + 1);
    for (int i = 1; i < n + 1; ++i) {
        parent[i] = i;
    }
    vector <int> sz(n + 1, 1); //размеры компонент связности -- сколько вершин
    int ans = 0;
    int max_sz = 1;
    for (int i = 0;i<m;++i){
        if (max_sz == n) {
            ans = i;
            break;
        }
        int a, b;
        cin >> a >> b;
        unite(a, b, parent, sz, max_sz);
        /*cout << "parent\n";
        for (auto x : parent) cout << x << ' ';
        cout << '\n';
        cout << "size\n";
        for (auto x : sz) cout << x << ' ';
        cout << '\n';
        cout << '\n';*/
    }
cout << ans << '\n';
}