#include <bits/stdc++.h>
char INPUT[] = "HelloWorld.inp";
char OUTPUT[] = "HelloWorld.outp";
const int MAX_N = 100 + 11;
const int MAX_K = 1000 + 111;
int main(void) {
  int n, k;
  scanf("%d%d", &n, &k);
  int x[MAX_N], y[MAX_N];
  for (int id = 0; id < n; ++id) {
    scanf("%d%d", &x[id], &y[id]);
  }
  double result = 0.0;
  for (int id = 1; id < n; ++id) {
    double temporary = 0.0;
    temporary += (x[id] - x[id - 1]) * (x[id] - x[id - 1]);
    temporary += (y[id] - y[id - 1]) * (y[id] - y[id - 1]);
    temporary *= k * k;
    result += sqrt(temporary) / 50.0;
  }
  printf("%lf", result);
  return 0;
}
