#include <cstdio>
#include <cmath>
#include <vector>
struct Point {
int x;
int y;
};
int main() {
std::vector<Point> bundle;
int N;
int R;
scanf(" %d %d", &N, &R);
for (int i = 0; i < N; ++i) {
int x;
int y;
scanf(" %d %d", &x, &y);
Point p;
p.x = x;
p.y = y;
bundle.push_back(p);
}
if (N == 2) {
double dis = sqrt((bundle[0].x - bundle[1].x) * (bundle[0].x - bundle[1].x) +
(bundle[0].y - bundle[1].y) * (bundle[0].y - bundle[1].y));
printf("%lf", 2 * dis + 2 * 3.14159265359 * R);
}
else {
printf("i don't know");
}
}
