#include <bits/stdc++.h>
using namespace std;
double dis(pair<int, int> p1, pair<int, int> p2) {
  return sqrt(pow(p1.first - p2.first, 2) + pow(p1.second - p2.second, 2)) /
         1000;
}
int main() {
  int n, k;
  pair<int, int> p;
  vector<pair<int, int> > vc;
  scanf("%d %d", &n, &k);
  double v = 0.05 / k, totalDis = 0;
  for (int i = 0; i < n; ++i) {
    scanf("%d %d", &p.first, &p.second);
    vc.push_back(p);
  }
  for (int i = 0; i < vc.size() - 1; ++i) {
    totalDis += dis(vc[i], vc[i + 1]);
  }
  cout << fixed << setprecision(10) << totalDis / v;
}
