vijos 1007 绕钉子的长绳子

#include<iostream>
#include<cmath>
#include<iomanip>
using namespace std;
const int maxn=110;
const double pi=3.14159;
double x[maxn],y[maxn];
int main(){
    int n;
    double ans=0,r;
    cin>>n>>r;
    cin>>x[1]>>y[1];
    for(int i=2;i<=n;++i){
        cin>>x[i]>>y[i];
        ans+=sqrt((x[i]-x[i-1])*(x[i]-x[i-1])+(y[i]-y[i-1])*(y[i]-y[i-1]));
    }
    ans+=sqrt((x[n]-x[1])*(x[n]-x[1])+(y[n]-y[1])*(y[n]-y[1]));
    ans+=pi*2*r;
    cout<<fixed<<setprecision(2)<<ans;
    return 0;
}