$n\le 100$，floyd 方便好写

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100;
int n, m, s, t;
int x[MAXN + 5], y[MAXN + 5];
double dis[MAXN + 5][MAXN + 5];
double len(int u, int v)
{
    return sqrt((x[u] - x[v]) * (x[u] - x[v]) +
                (y[u] - y[v]) * (y[u] - y[v]));
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    // 输入
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> x[i] >> y[i];
    cin >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            dis[i][j] = 100 * 20000;
    for (int i = 1; i <= m; i++)
    {
        int u, v;
        cin >> u >> v;
        dis[u][v] = min(dis[u][v],
                        len(u, v));
        dis[v][u] = dis[u][v];
    }
    cin >> s >> t;
    // floyd
    for (int k = 1; k <= n; k++)
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++)
                dis[i][j] = min(dis[i][j],
                                dis[i][k] + dis[k][j]);
    // 输出
    cout << fixed << setprecision(2) << dis[s][t] << "\n";
    return 0;
}