#include 
#include 
#include 
using namespace std;
const int maxn = 1e5 + 10;
const double INF = 2e9;
vector > graph[maxn];
int n, m;
struct node {
    int idx;
    double cost;
    node () {}
    node(int _idx, double _cost) {
        idx = _idx;
        cost = _cost;
    }
    bool operator < (const node & tmp) const {
        return cost > tmp.cost;
    }
};
void dijkstra(int S, int E) {
    vector dist(n, INF);
    vector visited(n, false);
    
    dist[S] = 0;
    priority_queue pq;
    pq.push(node(S, 0));
    
    while(!pq.empty()) {
        node c = pq.top();
        pq.pop();
        
        if(visited[c.idx]) continue;
        visited[c.idx] = true;
        
        for(pair tmp : graph[c.idx]) {
            int neighbour = tmp.first;
            double weight = tmp.second;
            
            if(!visited[neighbour] and c.cost + weight < dist[neighbour]) {
                pq.push(node(neighbour, c.cost + weight));
                dist[neighbour] = c.cost + weight;
            }
        }
    }
    printf("%.6lf\n", dist[E]);
}
int main() {
    int t;
    cin >> t;
    vector > v;
    for(int i = 0; i < t; i++) {
        double x, y;
        cin >> x >> y;
        v.push_back(make_pair(x, y));
    }
    for(int i = 0; i < t; i++) {
        for(int j = 0; j < t; j++) {
            double d = sqrt((v[i].first - v[j].first) * (v[i].first - v[j].first) + (v[i].second - v[j].second) * (v[i].second - v[j].second));
            if(d <= 10) {
                graph[i].push_back(make_pair(j, d));
                graph[j].push_back(make_pair(i, d));
                
            }
        }
    }
    
    n = t;
    dijkstra(0, n - 1);
    
    return 0;
}
/*
 5 5
 1 2 2
 2 3 4
 1 3 2
 3 4 5
 4 5 6
 **/