#include <iostream>
#include <iomanip>
#include <cmath>
using std::cin;
using std::cout;
using std::endl;
using std::setprecision;
using std::fixed;
int main()
{
    int n;
    double r,s=0,x,y,x0,y0,xn,yn;
    cin >> n >> r;
    if (n==1) {
        cin >> x >> y;
    }
    if (n>1) {

            cin >> x >> y;
    for (int i=1;i<=n-1;i++) {
    cin >> x0 >> y0;
    s=s+sqrt((x0-x)*(x0-x)+(y0-y)*(y0-y));
    x=x0;y=y0;
    }
    s=s+sqrt((xn-x)*(xn-x)+(yn-y)*(yn-y));
            }
s=s+2*3.1415*r;
cout << fixed << setprecision(2) << s << endl;

    return 0;
}

DEV-C++ 5.11

Edited by author 04.06.2017 12:53

Missed xn=x,  yn=y.
 http://ideone.com/PnKMSH

Thank you. I feel very sorry for such a stupid mistake...