計算Pi

long a=10000, b, c=2800, d, e, f[2801], g;
main() {
  while( b-c )
     f[b++] =a/5;
  while(d = 0 , g = c*2){
     b = c;
     while(d += f[b]*a, f[b] = d%--g, d /= g--, --b) d*=b;
     c -= 14;
     printf("%.4d", e+d/a);
     e = d%a;
  }
}