#include <stdio.h>
#include <math.h>
#define M_PI 3.14159

int main() {
  int N;
  float R, result = 0;
  scanf("%d", &N);
  scanf("%f", &R);
  if (N == 1) {
    result = 2 * R * M_PI;
  }
  else
  {
  float nails[N][2];

  for (int i =  0; i < N; i++) {
    for (int j = 0; j < 2; j++) {
      scanf("%f", &nails[i][j]);
    }
  }

  for (int i = 1; i <= N; i++) {
   result += sqrt((nails[i][0] - nails[i - 1][0]) * (nails[i][0] - nails[i - 1][0]) + (nails[i][1] - nails[i - 1][1]) * (nails[i][1] - nails[i - 1][1]));
}

  result += (M_PI * 2 * R);

  }
    printf("%.2f", result);
  return 0;
}

Edited by author 11.09.2018 16:32