Two blocks ($m = 0.5 \mathrm {~kg}$ and $M = 4.5 \mathrm {~kg}$) are arranged on a horizontal frictionless table as shown in the figure. The coefficient of static friction between the two blocks is $\frac { 3 } { 7 }$. Then the maximum horizontal force that can be applied on the larger block so that the blocks move together is $N$. (Round off to the Nearest Integer) [Take $g$ as $9.8 \mathrm {~m} \mathrm {~s} ^ { - 2 }$]