#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, ki;
  cin >> n >> ki;
  float res = 0, k[n][2];
  for (int i = 0; i < n; i++) {
    cin >> k[i][0] >> k[i][1];
    if (i > 0)
      res += ki * (sqrt((k[i][0] - k[i - 1][0]) * (k[i][0] - k[i - 1][0]) +
                        (k[i][1] - k[i - 1][1]) * (k[i][1] - k[i - 1][1])));
  }
  cout << fixed << setprecision(6) << res / 50;
}
