ACM 10589 - Area

#include <stdio.h>

int main()
{
    double N, a, x, y, i, in;
    while (1)
    { 
        scanf("%lf %lf", &N, &a);
        if (N == 0 && a == 0) break;
        in = 0;
        for (i = 0 ; i < N; i++)
        {
            scanf("%lf %lf", &x, &y);
            if (x*x + y*y < a*a && x*x + (a-y)*(a-y) < a*a &&
                (a-x)*(a-x) + (a-y)*(a-y) < a*a && (a-x)*(a-x) + y*y < a*a)
            in ++; 
        }     
        printf("%.5lf\n", (in/N)*a*a);     
    }
    return 0;
}

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