#include <bits/stdc++.h>
using namespace std;
const int N = 510;
struct Node{
    double x,y;
};
struct Edge{
    int x,y;
    double weight;
};
int father[N];
int height[N];
double Distance(double x1,double y1,double x2,double y2){
    double distance;
    distance = sqrt(pow(x1-x2,2)+ pow(y1-y2,2));
    return distance;
}
void Init(int n){
    for (int i = 0; i < n; ++i) {
        father[i] = i;
        height[i] = 1;
    }
}
int Find(int x){
    if (father[x] != x)
        father[x] = Find(father[x]);
    return father[x];
}
void Union(int x,int y,double weight,double &D,int &sum){
    int root_x = Find(x);
    int root_y = Find(y);
    if (root_x != root_y && sum>0){
        if (height[root_x] < height[root_y])
            father[root_x] = root_y;
        else if (height[root_x] > height[root_y])
            father[root_y] = root_x;
        else if (height[root_x] > height[root_y]){
            father[root_x] = root_y;
            height[root_y]++;
        }
        --sum;
    }
    if (sum == 0)
        D = weight;
}
bool comp(Edge lhs,Edge rhs){
    return lhs.weight < rhs.weight;
}
vector<Node> myNode;
vector<Edge> myEdge;
int main(){
    int S,P; //S个有线电话，P个哨所
    scanf("%d%d",&S,&P);
    Init(P);
    for (int i = 0; i < P; ++i) {
        Node node;
        scanf("%lf%lf",&node.x,&node.y); //每个结点的坐标
        myNode.push_back(node);
    }
    int edge_min = P-1; //P个哨所的最小生成树有P-1条边
    int edge_add = edge_min - (S-1); //现在只有S个有线电话(可以连接S-1条边)，那么还需加多少个无线电话,距离要尽可能的短
    for (int i = 0; i < P; ++i) {
        Edge edge;
        edge.x = i;
        for (int j = 0; j < P && j != i; ++j) {
            edge.y = j;
            edge.weight = Distance(myNode[i].x,myNode[i].y,myNode[j].x,myNode[j].y);
            myEdge.push_back(edge);
        }
    }
    double D = DBL_MAX;
    sort(myEdge.begin(),myEdge.end(),comp);
    for (int i = 0; i < myEdge.size(); ++i) {
        Edge edge = myEdge[i];
        Union(edge.x,edge.y,edge.weight,D,edge_add);
        if (D != DBL_MAX)
            break;
    }
    printf("%.2lf",D);
}