string.cpp

#include <iostream>
#include <cmath>
#define PI 3.1415926

using namespace std;

int main(){

    int n;
    double r, x0, y0, x1, y1, x2, y2, ans = 0;
    cin >> n >> r;
    ans += 2 * PI * r;
    if (n == 1){
        cout << (floor(ans * 100 + 0.5)) / 100. << endl;
        return 0;
    }
    cin >> x0 >> y0;
    x1 = x0, y1 = y0;
    for (int i = 1; i < n; i++){
        cin >> x2 >> y2;
        ans += sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
        x1 = x2;
        y1 = y2;
    }
    ans += sqrt((x2 - x0) * (x2 - x0) + (y2 - y0) * (y2 - y0));
    cout << (floor(ans * 100 + 0.5)) / 100. << endl;

    return 0;
}