#include <cstdio>
#include <cmath>
double a[101],b[101];
int main(){
int n;double r;
scanf("%d%lf",&n,&r);
for(int i(1);i<=n;++i)
{scanf("%lf%lf",&a[i],&b[i]);}

double ans(sqrt(pow((a[1]-a[n]),2)+pow((b[1]-b[n]),2)));
for(int i(2);i<=n;++i)
ans+=sqrt(pow((a[i]-a[i-1]),2)+pow((b[i]-b[i-1]),2));

ans+=3.1415926535898*2*r;
printf("%.2lf",ans);
return 0;
}