#include <bits/stdc++.h>
using namespace std;
template <typename T>
T in() {
  char ch;
  T n = 0;
  bool ng = false;
  while (1) {
    ch = getchar();
    if (ch == '-') {
      ng = true;
      ch = getchar();
      break;
    }
    if (ch >= '0' && ch <= '9') break;
  }
  while (1) {
    n = n * 10 + (ch - '0');
    ch = getchar();
    if (ch < '0' || ch > '9') break;
  }
  return (ng ? -n : n);
}
template <typename T>
inline T POW(T B, T P) {
  if (P == 0) return 1;
  if (P & 1)
    return B * POW(B, P - 1);
  else
    return (POW(B, P / 2) * POW(B, P / 2));
}
template <typename T>
inline T Gcd(T a, T b) {
  if (a < 0) return Gcd(-a, b);
  if (b < 0) return Gcd(a, -b);
  return (b == 0) ? a : Gcd(b, a % b);
}
template <typename T>
inline T Lcm(T a, T b) {
  if (a < 0) return Lcm(-a, b);
  if (b < 0) return Lcm(a, -b);
  return a * (b / Gcd(a, b));
}
long long Bigmod(long long base, long long power, long long MOD) {
  long long ret = 1;
  while (power) {
    if (power & 1) ret = (ret * base) % MOD;
    base = (base * base) % MOD;
    power >>= 1;
  }
  return ret;
}
bool isVowel(char ch) {
  ch = toupper(ch);
  if (ch == 'A' || ch == 'U' || ch == 'I' || ch == 'O' || ch == 'E')
    return true;
  return false;
}
template <typename T>
long long int isLeft(T a, T b, T c) {
  return (a.x - b.x) * (b.y - c.y) - (b.x - c.x) * (a.y - b.y);
}
long long ModInverse(long long number, long long MOD) {
  return Bigmod(number, MOD - 2, MOD);
}
bool isConst(char ch) {
  if (isalpha(ch) && !isVowel(ch)) return true;
  return false;
}
int toInt(string s) {
  int sm;
  stringstream second(s);
  second >> sm;
  return sm;
}
int head[802 + 10], par[802 + 10];
double dis[802 + 10];
bool chk[802 + 10];
struct Edge {
  int u, v, cap, next;
  double cost;
  Edge() {}
  Edge(int a, int b, int c, double d, int e) {
    u = a, v = b, cap = c, cost = d, next = e;
  }
};
Edge edge[2 * 802 * 802];
int NE;
void init(int n) {
  for (int i = 0; i <= n; i++) head[i] = -1;
  NE = 0;
}
void addEdge(int u, int v, int cap, double cost) {
  edge[NE] = Edge(u, v, cap, cost, head[u]);
  head[u] = NE++;
  edge[NE] = Edge(v, u, 0, -cost, head[v]);
  head[v] = NE++;
}
int spfa(int src, int sink, int tot) {
  queue<int> Q;
  for (int i = 0; i <= tot; i++)
    par[i] = -1, chk[i] = false, dis[i] = 2000000000;
  Q.push(src);
  dis[src] = 0.0;
  chk[src] = true;
  while (!Q.empty()) {
    int u = Q.front();
    Q.pop();
    chk[u] = false;
    for (int i = head[u]; i != -1; i = edge[i].next) {
      int v = edge[i].v;
      double w = edge[i].cost;
      if (edge[i].cap > 0 && dis[v] > dis[u] + w) {
        dis[v] = dis[u] + w;
        par[v] = i;
        if (!chk[v]) {
          chk[v] = true;
          Q.push(v);
        }
      }
    }
  }
  if (par[sink] == -1) return 0;
  int cap = 2000000000;
  for (int i = par[sink]; i != -1; i = par[edge[i].u])
    cap = min(cap, edge[i].cap);
  for (int i = par[sink]; i != -1; i = par[edge[i].u])
    edge[i].cap -= cap, edge[i ^ 1].cap += cap;
  return cap;
}
pair<int, double> min_cost_flow(int src, int sink, int tot) {
  double ret = 0;
  int flow = 0;
  while (true) {
    int cap = spfa(src, sink, tot);
    if (cap == 0) break;
    flow += cap;
    ret += (cap * 1.0 * dis[sink]);
  }
  return make_pair(flow, ret);
}
pair<int, int> a[802];
double Dist(int i, int j) {
  double x = (a[i].first - a[j].first) * (a[i].first - a[j].first);
  x += (a[i].second - a[j].second) * (a[i].second - a[j].second);
  x = sqrt(x);
  return x;
}
int main() {
  int n;
  n = in<int>();
  for (int i = 1; i < n + 1; i++) {
    a[i].first = in<int>(), a[i].second = in<int>();
  }
  init(n * 2 + 4);
  int src = 0, des = (n * 2) + 1;
  for (int i = 1; i < n + 1; i++) {
    addEdge(0, i, 2, 0);
    addEdge(i + n, des, 1, 0);
  }
  for (int i = 1; i < n + 1; i++) {
    for (int j = 1; j < n + 1; j++) {
      if (a[i].second > a[j].second) {
        double dst = Dist(i, j);
        addEdge(i, j + n, 1, dst);
      }
    }
  }
  pair<int, double> ans = min_cost_flow(src, des, des);
  if (ans.first != (n - 1)) {
    printf("-1\n");
  } else {
    printf("%.10lf\n", ans.second);
  }
  return 0;
}
