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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll shift=1e7;

struct point{
    ll x,y;
    point(){}
    point(ll x,ll y):x(x),y(y){}
};
 ll dist(point a,point b){
    ll x=abs(a.x-b.x);
    ll y=abs(a.y-b.y);
    return x*x+y*y;
}
int len(ll x){
    if(!x)return 1;
    int ret=0;
    while(x)x/=10,ret++;
    return ret;
}
int main(){
    ll N,a;
    while(true){
        cin>>N>>a;
        a*=shift;
        if(!N)return 0;

        ll M=0;
        point temp;
        for(int i=0;i<N;i++){
           double d1,d2;
           cin>>d1>>d2;

            temp.x=(ll)(d1*shift);
            temp.y=(ll)(d2*shift);

            ll dist1=dist(point(0,0),temp);
            ll dist2=dist(point(0,a),temp);
            ll dist3=dist(point(a,0),temp);
            ll dist4=dist(point(a,a),temp);
            ll D=a*a;
            if(dist1<=D && dist2<=D && dist3<=D && dist4<=D )M++;

        }
        ll A = M * a/shift * a/shift;

        printf("%lld.",A/N);

        int dec=0;
        ll res2=A%N;
        int len1=len(N)-1;
        int len2=len(res2);

        for(int i=0;i<len1-len2;i++)printf("0"),dec++;
        printf("%lld",A%N),dec+=len(A%N);
        for(int i=0;i<5-dec;i++)printf("0");
        printf("\n");

    }
    return 0;
}