求凸包,算周長,加上2*Pi*r即得所求
//============================================================================
// Name : hello.cpp
// Author : key
// Version : 8
// Copyright : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================
#include <iostream>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <string>
#include <algorithm>
using namespace std;
#define NUM_INF 0XFFFFF
/*==================================================*\
| Graham 求凸包 O(N * logN)
| CALL: nr = graham(pnt, int n, res); res[]爲凸包點集;
\*==================================================*/
struct point {
double x, y;
}pnt[1010],res[1010];
bool mult(point sp, point ep, point op){
return (sp.x - op.x) * (ep.y - op.y)
>= (ep.x - op.x) * (sp.y - op.y);
}
bool operator < (const point &l, const point &r){
return l.y < r.y || (l.y == r.y && l.x < r.x);
}
int graham(int n){
int i, len, k = 0, top = 1;
sort(pnt, pnt + n);
if (n == 0) return 0; res[0] = pnt[0];
if (n == 1) return 1; res[1] = pnt[1];
if (n == 2) return 2; res[2] = pnt[2];
for (i = 2; i < n; i++) {
while (top && mult(pnt[i], res[top], res[top-1]))
top--;
res[++top] = pnt[i];
}
len = top; res[++top] = pnt[n - 2];
for (i = n - 3; i >= 0; i--) {
while (top!=len && mult(pnt[i], res[top],
res[top-1])) top--;
res[++top] = pnt[i];
}
return top; // 返回凸包中點的個數
}
double dis(point a,point b)
{
return sqrt(double((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)));
}
int main()
{
int n;
double r;
int i;
double Pi = acos(-1);
double sum;
scanf("%d%lf",&n,&r);
for(i=0;i<n;i++)
{
scanf("%lf%lf",&pnt[i].x,&pnt[i].y);
}
n = graham(n);
sum = dis(res[0],res[n-1]);
for(i=1;i<n;i++)
{
sum += dis(res[i],res[i-1]);
}
printf("%.0f\n",sum+Pi*(2.0*r));
return 0;
}