#include<stdio.h>

double distance( double x1, double y1, double x2, double y2 )
{
    return (x1-x2)*(x1-x2) + (y1-y2)*(y1-y2);
    
}

int main()
{
    int N, a;
    while( scanf( "%d%d", &N, &a ) != EOF && N != 0 && a != 0 )
    {
        int i;
        int M = 0;
        for( i = 0 ; i < N ; i++ )
        {
            double x, y;
            scanf( "%lf%lf", &x, &y );
            if( distance( x, y, 0.0, 0.0 ) <= (double)(a*a) )
                if( distance( x, y, 0.0, (double)a ) <= (double)(a*a) )
                    if( distance( x, y, (double)a, (double)a ) <= (double)(a*a) )
                        if( distance( x, y, (double)a, 0.0 ) <= (double)(a*a) )
                            M++;
        }
        printf( "%.5lf\n", (double)M/(double)N*(double)a*(double)a );
    }
    return 0;
}