In Young’s double-slit experiment, two wavelengths $\lambda_1 = 780 \, \text{nm}$ and $\lambda_2 = 520 \, \text{nm}$ are used to obtain interference fringes. If the $n^{\text{th}}$ bright fringe due to $\lambda_1$ coincides with the $(n + 1)^{\text{th}}$ bright fringe due to $\lambda_2$, then the value of $n$ is