Interference is observed due to two coherent sources $\mathrm{A}$ and $\mathrm{B}$ having zero phase difference separated by a distance $4\mathrm{\lambda }$ along the $\mathrm{y}$-axis, where $\mathrm{\lambda }$ is the wavelength of the source. A detector $\mathrm{D}$ is moved on the positive $\mathrm{x}$-axis. The number of points on the $\mathrm{x}$-axis excluding the points $\mathrm{x}=0$ and $\mathrm{x}=\mathrm{\infty }$ at which maximum will be observed is