C++ :

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#define INF 999999.0
using namespace std;

struct Outpost{
    int x, y;
}O[501];
int cmp(double a, double b){
    return a > b;
}
int s, p;
double dist[501][501], d[501];
char vis[501];
void prim(){
    int i, j, k, mini, minj;
    double min;
    vis[1] = mini = 1;
    for(i = 1; i <= p; i++){
        min = INF;
        for(j = 1; j <= p; j++){
            if(!vis[j]){
                if(dist[mini][j] < d[j]){
                    d[j] = dist[mini][j];
                }
                if(d[j] < min){
                    min = d[j];
                    minj = j;
                }
            }
        }
        mini = minj;
        vis[mini] = 1;
    }
}
int main(){
    int k, i, j, x, y;
    scanf("%d", &k);
    while(k--){
        scanf("%d%d", &s, &p);
        memset(vis, 0, sizeof(vis));
        memset(O, 0, sizeof(O));
        for(i = 1; i <= p; i++){
            scanf("%d%d", &O[i].x, &O[i].y);
            d[i] = INF;
        }
        for(i = 1; i <= p; i++){
            for(j = 1; j <= i; j++){
                x = O[i].x-O[j].x;
                y = O[i].y-O[j].y;
                dist[i][j] = dist[j][i] = sqrt(x*x + y*y);
            }
        }
        prim();
        sort(d+1, d+p+1);
        printf("%.2f\n", d[p-s]);
    }
    return 0;
}