private static int Search(int node, bool[] visited, List<List<int>> nextNodes)
{
    int citiesInGroup = 1;
    visited[node] = true;

    foreach (int item in nextNodes[node])
    {
        if (!visited[item])
            citiesInGroup += Search(item, visited, nextNodes);
    }

    return citiesInGroup;
}

public static long roadsAndLibraries(int n, int c_lib, int c_road, List<List<int>> cities)
{
    if (c_lib <= c_road)
        return (long)c_lib * n;

    long cost = 0;
    bool[] visited = new bool[n + 1];
    List<List<int>> nextNodes = new List<List<int>>(n + 1);

    for (int i = 0; i <= n; i++)
    {
        nextNodes.Add(new List<int>());
    }

    foreach (var cityPair in cities)
    {
        int indexFor0 = cityPair[0];
        int indexFor1 = cityPair[1];
        nextNodes[indexFor0].Add(indexFor1);
        nextNodes[indexFor1].Add(indexFor0);
    }

    for (int i = 1; i <= n; i++)
    {
        if (!visited[i])
        {
            int citiesInGroup = Search(i, visited, nextNodes);
            cost += c_lib + (long)(citiesInGroup - 1) * c_road;
        }
    }

    return cost;
}